Minimum Descent Altitude and How to Get There

by Wally Moran on May 26, 2010

In the Pilotworkshops.com IFR Proficiency series, titled “Descending on a non precision approach” respected flight instructor Rod Machado explains the benefit of descending to MDA early on non precision approaches. Rod makes the point that getting to the minimum descent altitude (MDA) prior to the visual descent point (VDP) allows the pilot a greater opportunity to see the required visual references during low visibility and therefore a better chance of landing. Rod advocates a dive and drive technique rather than a stabilized approach that plans to reach MDA at or near the VDP. He further advocates, in some cases, descending below the GPS advisory vertical guidance where available to get to MDA sooner.

While I realize disagreeing with Rod Machado about flying is like arguing with the Pope about religion, I would like to present a case for making all of our approaches as stabilized as possible and never descending below the GPS advisory vertical guidance when executing a non precision approach.

It is, of course necessary, to arrive at MDA in time to make a normal approach and landing but, in my view, there is little advantage to being there well before the VDP. This simply puts the pilot in the most dangerous area of the approach for a longer time. Yes, charted minimums provide protection but, a mistake at MDA gives little time for correction while a mistake at a higher altitude leaves greater margin. The lower one goes, the greater chance of hitting things that are fastened to the ground, therefore why be in such a hurry to get down there.

I prefer to begin my descent with a good solid 750 FPM. Since that is typically more than needed, I can shallow the descent as I approach MDA and the VDP if one is available. Then as I break out, I merely adjust my descent for landing as I would on any approach. In my view, this makes a much more stabilized approach. While the dive and drive technique may get you in one day when the visibility is at the very minimum, I am happy to give up that small advantage for the benefit of a more stabilized approach. A dive and drive approach is by definition unstable at least until the VDP.

Should the approach have an advisory glide slope as many do now, as an instructor, I would not teach to deliberately fly below it. First of all teaching to fly below a glide slope is just encouraging a bad habit and not a good thing to teach. Further we know that approaches with vertical guidance have less risk than those without vertical guidance so why give up a margin of safety if you can avoid it.

History has shown that non precision approaches with step down procedures, that is, intermediate level offs prior to MDA, are the most dangerous. Following the advisory glide slope if available will guarantee that one complies with those restrictions. That, if nothing else, will keep me on that glide slope.

So with all due respect to the Pope of our church of flying things, I prefer to make a stabilized approach adjusting my descent to arrive at MDA as near to the VDP as possible and do  not advocate deliberately going below the advisory glide slope.

What say others?

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BM September 3, 2010 at 7:55 am

My question is, how many approaches have you flown to the absolute minimums, that min vic and ceiling? when flying ifr anywhere with weather below alternate minimums i plan for 2 approaches then off to an alternate. I have been flying 10 years and the number of times that two approaches hasn’t been enough is far a few between. In the order of maybe 10 a year.

Just my two bob
BM

Roger Halstead July 19, 2010 at 3:17 am

I have to agree with Rod 100%. To me, stabilized still lets me make that descent early.
Sounds contradictory doesn’t it, but it’s not

I set up my approach speed in the Debonair/Bonanza at 120 MPH which is 17″ and 2400 RPM. AT the FAF I dump the gear, while holding airspeed. That will give me 700 fpm at 120 MPH. If I need steeper, each 1″ of MP will give me 100 fpm. In the Deb there is no trim change with power change. If I go to 12″ that gives me 1200 fpm. Coming up on MDA I just bring the power back up to 21 or 22″ depending on the day. This allows me to maintain 120 MPH through the approach and into the circle to land. Going into the circle to land I usually bring the power all the way up to 24″ X 2400. This gives me plenty of power to maneuver at 500′ AGL. As I approach 30 to 40 degrees within the runway heading the power comes back to 12″, prop to fine. That steep turn bleeds off speed fast. and still lets me set down on the touchdown zone.

To me the stabilized approach or pattern is far over rated although it’s a great learning tool for students either primary or instruments, “pilots” should have already graduated beyond having to fly a stabilized pattern or approach. I see enough of those who have to fly a pattern the way they do at home, at Oshkosh, to last until the next year. Like at Osh, a pilot needs to be able to adjust speed and power when told, fly base where told and “land on a spot” 10 to 20 feet across.

Getting down early on the instrument approach lets you see what’s at MDA AND it gives you as much as 3 more miles to transition to visual and get ready for the landing. Flying a stabilized profile gives you only seconds to transition and that’s just about the time ATC is giving instructions.

Jean P July 17, 2010 at 5:07 pm

The airlines gave up on the “Dive and Die” approach long ago. When my airline started using the stabilized approach I was on the MD-80. At that time the oldest airplane in the fleet. Everyone else just engaged V Nav and let the box do the work. We had to calculate the VDP and descent rate. You have to realize airline pilots have to go to the simulator every six months and play “You bet your job”. Only the first few minutes of the sim ride are with both ( three on the 72 ) engines turning. Imagine a dive and drive on one engine in a 737-900. Every power change requires two trim changes. Leveling off at MDA requires powering up ( way up ) the good engine, rolling trim towards the good engine ( or adding a lot more rudder ) and sometime a pitch trim change since the engines are way below the center of gravity. A few seconds later you reach your VDP so now its power back, adjust rudder trim and adjust pitch trim. At 100 feet the old fuel truck pulls on to the runway and it’s go around time. Hit TOGA, big power change on the good engine, hold the nose down pitch trim button and grab for the rudder trim knob. Call for flaps 15 when the FO calls positive rate and climb to 400′ then call for heading select or LNAV. Retract the flaps on schedule at 1000′ Then call for the after takeoff checklist and the single engine approach and land checklist and do it all over again for several hours. This all takes place at 03:00 in the morning since the airline rents the sim to other people during daylight hours.

Doing a constant rate descent with a good FMC is no different than an ILS. The box will take you right to the VDP and the auto throttles will keep you right on V Ref plus 5. But how many piston powered GA aircraft have an FMC. We did a lot of mental calculations on the 80 but it always seemed to work out to 750 FPM at 145 knots. The MD-80 does have auto throttles. It also has a very good auto land but you have to have an ILS to use it. All you have to do on your aircraft is go down the glide slope of an ILS at V Ref. plus 10 and see what your VSI reads. Use that same speed and descent rate for a constant rate descent and it should bring you right to the VDP ( not the MAP ). If the plate doesn’t have a VDP you will have to calculate one using the old 300′ per mile formula. I know doing it like the airlines do it doesn’t hold much water with some of you but it does mean every approach is done the same and some of you will be airline pilots in the future. I started in PA-28s and 150s and flew GA for 13 years before the majors.

Fred Zervos July 17, 2010 at 8:01 am

Returning to Mitchel Field in September 1928, he assisted in the development of fog flying equipment. He helped develop the now almost universally used artificial horizontal and directional gyroscopes and made the first flight completely by instruments. He attracted wide newspaper attention with this feat of “blind” flying and later received the Harmon Trophy for conducting the experiments.

Who was this guy? I wonder what technique he would use for the non precision approach?

Elliott July 16, 2010 at 8:07 pm

Is this horse dead yet? No? Well then I’ll keep whipping him. Several things come to mind.

First, as a couple folks already stated, at DA, you are entitled to go past that altitude as you initiate the missed approach, but at MDA, you may NOT go below it during a missed approach. Therefore, you MUST give up some normally available altitude if you use the “glideslope” on a non-precision approach. I have seen many times in my 20 years of IFR flying where 50 feet made the difference between getting in and not seeing the airport at all.

Second, I haven’t seen very many jets and airliners at most of the 12,000 or so airports in the US. They usually get to land at airports with lots of approach lights, nicely painted runways, and obstacles in the approach path heavily controlled. SO, using CANPA is the way to go for them. Furthermore, they generally have the avionics to assist the pilot in selecting and flying a “stabilized approach” like a pretend glidepath. The vast majority of the 40 some makes and models I’ve PIC time in don’t have such avionics.

Which leads me to a 3rd point, just how accurate is your “stabilized approach” when you select your descent rate prior to the FAF based upon a math model “guesstimate”. So, you are off a bit, and hit the MDA + 50 feet, 1/4 mile outside a VDP, then what? Exactly, you still wind up having to level off or go missed early.

Fourth point, on an ILS, assuming I keep the needles married up, if If I break out at minimums, the runway is dead ahead, lined up, and all I have to do is select my aimpoint, check the wheels down and locked, and land. Like mentioned above, if you do the pretend glideslope thing, there is no such guarantee, and you don’t have to be very far off in your calculations to be high, fast, and offline, really close to the runway. Talk about scary!!! You have mere seconds to do the right thing, and tired pilots anxious to get on the ground all too frequently make the wrong choice.

Number 5, since most FAF’s are less than 6 miles from the runway, you would have to be pretty stupid to “dive” to the MDA so hard as to leave you 4-5 miles of slogging it out 400 feet AGL. I can’t remember having to fly at MDA for more than a couple miles prior to reaching MAP, and since few non-precision approaches have a visibility minimum of less than a mile, you knew weren’t going to be landing well prior to the MAP. I was taught, and I still teach, that you should not descend at a rate higher than the altitude you have to lose, and NEVER descend at more than 500 fpm below 1000 AGL. I descend on a non-precision approach at 800 – 1000 fpm until within 1000 feet of MDA, and then begin shallowing to 500 fpm, initiating level off 10% of my descent rate above MDA. Sure turbulence can be an issue, so then you add a cushion if you have to so you can stay above MDA. If you can’t hold MDA reliably, you shouldn’t be flying in the soup.

Having said all this, yes, I will adjust my descent rate as needed to minimize the time at MDA. But when properly flown, there is nothing unstabilized about descending to MDA prior to a VDP at all. The aircraft is under complete control, flying according to plan, and the successful outcome (safely reaching Mother Earth sooner or later) is NEVER in doubt, even if I have to miss the approach, do it again, and still have to divert.

jerry brown July 16, 2010 at 4:41 pm

Both Wally and Rod make valid points.

These are some items that I consider when flying a non-precision approach:
How I descend on the approach after crossing the FAF requires evaluating my current experience for the particluar approach perfomed. I review if I am familiar with this approach and if I know the surrounding terrain & obstacles. Am I flying in soft & smooth or hard & turbulent IFR? Day or night approach? Will I be fresh and alert or tired? What approach speed and descent rate will I use? What are my aircraft and support equipment capabilites (GPS, WAAS, Synthetic Vision, EFB, Traffic & etc.)? ATC Radar environment? What type of airport lighting is installed? In most cases larger non-towered airports with longer & wider runways are easier to pick out than smaller airports, especially if there is more than one runway. With that said, I was taught to fly down to and maintain the MDA until acquiring the airport or going missed, but in many cases I find that the stabilized descent to the MDA is easier for me.

DaveS July 16, 2010 at 3:19 pm

The oft-stated advantage of dive & drive is increased opportunity to catch a glimpse of the runway while cruising at the MDA, but I view that as glitter without gold. The “drive” part will often start at several times the min viz distance from the runway, so it helps only under fair-to-good conditions. It fails when the last low cloud is near the threshold, but gives no advantage if the runway is in sight beyond a reasonable normal letdown to touchdown distance. The one advantage of dive and drive to me is that its practitioners might help clear away some trees if they drift too low while straining to see the runway.

Osama Alhadi July 16, 2010 at 2:42 pm

Hi, all my friends and thank you for every thing , And ihope you are ( OK ) and Iwould like
to give me some caulculation ,fuel, dstance, for many aicraft,alt.
by the way, I invitatory some friend as a pilot to this website.
best wishes

Osama Alhadi July 16, 2010 at 2:40 pm

Hi, all my friends and thank you for every thing , And ihope you are ( OK ) and Iwould like
to give some caulculation ,fuel, dstance, for many aicraft,alt.
by the way, I invitatory some friend as a pilot to this website.
best wishes

Peter Horvat July 16, 2010 at 1:56 pm

Whatever turns your prop. both methods are acceptable depending on the severity of the clog

James Gallagher July 16, 2010 at 1:32 pm

I consider myself a perpetual student, and if can forgive a pun, my “CFI” is a Cessna 172. at this fun time in my life. AOPA is an incredible organization. thank you all, Jim

JUAN CARLOS ALMIRON July 16, 2010 at 11:15 am

HI ALL !!
I’M A PROSPECT 65 YEARS YOUNG WITH SOME FLIGHT SIM.EXPERIENCE AND RIGHT SEAT ON A SINGLES.MI COMMENT STARTS WITH :THE PILOT SHOULD LEARN AHEAD OF TIME THE ALTITUDE OF THE AIRPORT AND SORROUNDING LANDSCAPE .OR ADVISORIES ,FLAPS AND ENGINE SPEED ,SLOW DESCENT WILL GIVE OPORTUNITY TO VIEW, ALTITUD AGAIN,DISTANCE TO THE AIRPORT AND SORROUNDINGS !THEN APROACH TO LAND OR GO AROUND !! IF FUEL PERMITS !!. MAYBE IM WRONG A I WILL LIKE TO LEARN . IN THE ABOVE COMMENTS IT WAS NOT INCLUDDED COMUNICATIONS WITH THE AIRPORT TOWER?

Alex July 16, 2010 at 10:50 am

In heavy jet like light wt.aircraft with 2 pilots
The main issue here is the CRM and well training back ground.
4 eyes,2 know ledges,,,would result positively to safe approach down to VDP.
ILS is different than VOR approaches.
Unfortunately some IFR instructors like to see the results as in his level only.
The best and successful way in the advanced training stages,,is to teach communications..
1-let the pilot have a good briefing techniques,,,that would expose what in his/her mind and that would be easy to be corrected before conducting any approach,,
2- Approach briefing by the pilot flying would show what he/she need from the instructor as if he is a co-pilot.
Fly Safe
Alex

John Dormer July 16, 2010 at 10:15 am

I think both techniques have merit. In a mountainous area I would prefer a glide slope. If at sea level with low vis., I might want a controlled descent to be at MDA early. I think it is scenario dependent. Bottom line it is awareness, scan and preparation. Cockpit workload should drive the technique. If tasking is an issue and you are FMS equipped,shoot a coupled approach and monitor the heck out of your approach regardless of method. Planning is key.

Ed Williams July 16, 2010 at 10:03 am

Dive and drive has a huge advantage (in terms of successfully completing approaches to a landing) when lateral guidance is imprecise (eg VOR or NDB as opposed to LOC or GPS). Even with the needle centered, there’s no guarantee the runway will be dead ahead when you break out. Some non-precision approaches are little more than hunting licenses for the airport. The sooner you get to minimums, the longer you have to get your alignment corrected. A late breakout invites overly radical last-second maneuvering, a risky operation at best.

What should be avoided is high rates of descent close to the ground. If a steep angle of descent is required, use high rates of descent early in the approach and moderate them as you approach minimums. The level off at MDA is one of the most critical moments in the approach, often distracted by outside references. It’s better to make it a little easier by giving yourself extra time to do it.

larry Olson June 12, 2010 at 11:20 am

Warren,

I agree with you, this is a GA discussion, and that’s why I said the CANPA was not appropriate…. but could be used. One just looses a LOT of flexibility (and I believe safety) using it.

And, I have no problem following the advisory GS down, but would absolutely treat it as a non precision approach and level at the MDA and not use a DH. Personally, I prefer to get down early and have no problem descending faster than the advisory GS, to the appropriate altitude on the plane to have more time at minimums, especially if wx is at mins.

However, if it’s a high ceiling where I’d expect to break out well above mins. the GS works fine.

Warren Webb Jr June 8, 2010 at 8:47 pm

Larry,

Thanks for the clarification and I agree with you except I would still use the advisory glideslope as I mentioned before and I probably don’t dive quite as aggressively as you do. Actually I thought this was a discussion only on the lighter GA aircraft, so I guess I made a wrong assumtion on that.

Warren

Larry Olson June 7, 2010 at 8:14 am

Warren,
There is nothing wrong with Holgate’s CANPA approach. One can set it up appropriate for their plane, flaps or not, stabilized, front side of the power curve, and at a constant rate down. Also, you’d have a pretty good idea of the winds. And a lot of planes have FMS systems that can set this up on a Vnav profile and nail it. Or, one could use the advisory GS off the GPS.

HOWEVER, this is only appropriate for heavy jets, that don’t have a good record with dive and drive. I did the CANPA thing in the airline business, and not only worked will, it was required. For us GA guys, it’s totally inappropriate, and we would loose a lot of flexibility and probably miss a few approaches that could be easily made with the dive and drive method.

As for the comments about being way too low, miles from the airport….. if one is paranoid about that, it’s easy to do the math and plan on reading MDA about a mile from the miss, still allowing one time to assess the situation for the landing. Me, I want to be down early to have all the time I need. Being at 400 feet 3 miles out is fine, and still in protected air.

I’m a STRONG proponent of the dive and drive for anything that will fit in cat A or B approaches (less that 120K). Safer, easier and makes for a more successful approach.

Warren Webb Jr June 5, 2010 at 10:47 pm

John Holgate’s suggested stabilized approach in the landing configuration is interesting but I don’t think I’d care to use it. A few reasons – assume Skyhawk or similar type:

1. This means a transition from cruise speed to about 65 knots and full flaps in cloud.
2. In rough weather, the aircraft would be much more difficult to maintain in a stabilized state.
3. The aircraft would be on the edge of the backside of the power curve – especially in strong downdrafts this is not where you would want to be.
4. Calculating a descent angle of 300 feet per nm would sometimes get you close to desired position but since it’s really just an estimate, unknown headwinds or tailwinds would carry you to unknown positions and you would not really have a stabilized approach in the end to the VDP and threshhold.
5. Missed approaches from full flaps and 65 knots would not be any fun.

John Holgate June 5, 2010 at 3:00 am

A 3 degree (300 feet per nm) stabilised approach in the landing configuration down to the MDA, allows the pilot to fly the entire approach while concentrating on the primary task of flying and navigating the a/c.

At the MDA plus 50′ the decision to land or go around is made.
If the runway environment is sighted, the a/c continues on the stabilised approach path (with papi or vasi slope guidance if available) to touch down.
A missed approach is performed immediately if the runway environment is not sighted at the MDA plus 50′.

This CANPA (Constant angle non presision approach) has the advantages of:
1. Increased terrain clearance during most of the approach.
2. A stabilised approach resulting in better situational awareness.
3. Fuel and noise efficient

Loren Herren May 31, 2010 at 8:47 pm

Great discussion! During training we teach both methods, with an ever-present pair of reminders. First, how the approach will be flown is a matter to be planned well in advance, according to the time-tested rule of aviation – “it depends.” Newer students tend to want to fly “by the book” and get down to a published MDA sooner than later, but don’t consider that doing so leaves them well below 1000′ AGL for 4 – 5 miles over terra very firma. The margins at that altitude get pretty thin no matter where you fly. That said, an e-slope on the GPS offers a nice stabilized approach (though I also don’t want them to become overly reliant on the machine at the expense of their own thinking and ADM), and there is nothing wrong in using one if the pilot deems the conditions make this option the best one in the bag. Second, the planning should cover not only what the pilot should expect to see at MDA on the way in (particularly if shooting an approach on an inbound course offset from the intended landing runway centerline, or if working in an area with multiple airports or look-alikes), but how and when to determine that the reality and the plan do not match, and what to do about this if it occurs. Updating one’s SA is key. If there is legitimate risk of a tight squeeze of the ceiling at MDA, then a bit more time to recognize this might be in order, whereas a stabilized approach on a GPS slope means less messing around in the cockpit, but also means the pilot must be prepared to and then act on whatever they do or do not see when they arrive at the MDA at or just prior to the MAP. No matter the descent method selected, the pilot needs to remain mentally ahead of the situation and the airplane, and it’s that precious judgment that we’re constantly working to instill. Thanks for a great discussion and keep up the good work.

Warren Webb Jr May 29, 2010 at 9:15 pm

I’ve been teaching the ‘dive and drive’ nearly 30 years usually with a target of 800 fpm with the objective of not overshooting the VDP and creating a tricky or impossible descent angle to the runway. Another objective is to not miss an area of possibly higher cloud bases that would allow an appropriate initial descent from MDA, avoiding possibly lower cloud bases beyond the VDP and a Missed Approach. As long as you apply the 10 percent vertical speed rule of thumb, the leveloff is no different than any other. If you get to MDA really quickly, there can be some trade-off in that you may be in rough conditions much longer, and you may find it harder to establish visual contact with the runway environment (further out in low vis) or experience some disorientation because of the flatter angle to the runway.

Having flown a few approaches with GPS advisory vertical guidance, I’d have to say that’s one of the best things to ever come along. It is a beautiful thing how that glide slope will bring you in with a little cushion over step-down fixes and right into the threshhold including an advantageous downward viewing angle. I would definitely use it whenever it is available. I haven’t had an opportunity to fly a GPS advisory vertical guidance approach in weather near approach minimums. But when I eventually do, I will stay on that glideslope, and if I thought it were needed, somewhere further down there, I would gradually increase the rate of descent to get the glide slope needle trending upward, and then get a little earlier leveloff at MDA. That glideslope would be too great a tool not to use.

Great comments by all contributors. I’ve learned a lot.

Steve Lopez May 29, 2010 at 4:51 pm

Mr. Machado wears an airplane like a pair of pants and it is all I can do to fly one. I think I will stick to SOP. Standard Operating Procedures are not fool proof nor are they always the best course of action but they will reduce the kind of surprises that are not welcome.

Larry Olson May 29, 2010 at 12:14 pm

John Collins has it right.

First of all, let’s eliminate the safety thing… it is NOT more dangerous to do a dive and drive than an ILS for GA aircraft, per a study by the Mitre Corp with the FAA. In transport jets, yes, it is, but their safety is a whole different story for another page. They are different. Jets also require a stabilized approach, which may or may not be appropriate for GA.

Now, with the dive and drive, what you get is TIME to evaluate the situation… and there’s no rush. One can decide on which runway is most appropriate and how to execute the circle, if needed. You also, in a lot of cases, get lower minimums than you get with a precision approach.

As for how steep or the rate of descent, that would be determined by the speed at which the approach was flown and what was needed to accomplish the descent. There is no “maximum” rate or speed for pt 91 GA planes, however, it would be prudent to fly what is appropriate for one’s plane. Like Collins said, up to 6 deg is appropriate and safe for our GA planes, up to small turboprops.

Wally Moran May 29, 2010 at 7:07 am

What a great collection of good thoughts.

As in many things in aviation, there is more than one correct way to perform a task. As one commenter said, it may depend upon the airplane, the pilot, and the weather. Then it is up to the pilot to choose the technique that works best for him or her at the moment.
That’s called good pilot judgment.

I knew this topic would generate discussion and that is one reason I chose it. Discussions like this are an excellent learning tool for all pilots and I can say that I have learned a thing or two as a result of reading these comments.

Thanks to all for your thoughts and however you choose to get to MDA, Keep it safe!!

Wally

William Ashley May 29, 2010 at 4:21 am

American Airlines placed a MD80 in the trees in Hartford a several years ago causing
their instructors to adapt a policy of a steady, constant rate descent rate, stablized approach to the MDA. Once at minimums, if there was no visual of the ground, a go-around began immediately, ie., no real reason to hang around.
As an instructor in sim training and on the line, I observed, most of the problems our pilots had on non-precisions approaches that were too high of an approach speed causing higher rates of descents. Which was the problem at Hartford.

Roger Halstead May 29, 2010 at 3:21 am

I have to agree with rod and although stats may show this puts us in a dangerous position I find this approach to be comfortable, easy, and to me it’s stabilized.

I only have an old RNAV, VOR, and NDB. I use these and am comfortable with all three. I see no connection on the “step down” and misusing the ILS. With the ILS you have vertical guidance. I have none except on an ILS. Also what I’ve seen with vertical guidance it brings you to MDA over the end of the runway. I’d much rather be at MDA farther out. Then there are no real last second decisions. If I see nothing at MDA 3 or 4 miles out, I can pretty well plan on a missed. OTOH If I can see the airport at or above MDA from that far out, I can see the whole landing from there be it straight in or circling.

I fly the whole approach at 120 MPH (it’s an old airplane). When I reach the step down point, Altitude hold is off and I lower the gear. This gives me no change in airspeed or trim. (It’s a Debonair), but it does give me close to 800 fpm. Just prior to MDA I bring up the MP to about 23″ which will give me level flight. Altitude hold goes back on.

Sure I could hand fly it and often do, but why add extra work unless I’m just practicing. My old instructor used to make me fly that approach with only one radio, a step down hold and timed turns.

As far as obstacles you have to be pretty far off course to worry about them. Within the FAF I’ve never seen anything that sticks up to MDA. If your eyesight and radios don’t agree, *at least* one of them is wrong. With two navs that’s pretty easy to figure out. A hand held GPS will give confirmation. Always know ahead of time what to expect. As a student this can be difficult, but if you’ve been flying IFR a few years, it should be second nature even if ATC makes a mistake you should recognize it. I’ve been vectored for traffic avoidance while in the soup and then forgotten. I’ve been cleared for a circle to land right in front of departing traffic and I’ve been told to “follow the guy ahead” when I could barely see the prop. Down at KFNT there is a note on the chart to not use visual clues, but stay on the ILS due to parking lot lights looking like airport lights.

Howie Keefe May 29, 2010 at 1:58 am

The”dive and drive”, especially as depicted on Jepp’s ancient style plate, is from the slow moving DC-3 era of 120 mph approaches. Try that slow speed at a major airport and you’ll hear the cussing of the heavies “go arounds” behind you! Even at my P-51 approach speeds of 150 mph and the full flaps for a 90 mph TD I’ve been cursed out. Today’s faster planes make a stabilized AS the only sensible thing. Rod must be doing his approaches in a 152 at CTAF airports only—-in flat land country at that. He’s a friend. I’ll have to educate him.

Andrew May 28, 2010 at 9:46 pm

I think this discussion is very healthy, as the last thing you want to do is end up at MDA with marginal visibility and not have a clear plan.
I would say, both techniques are valid but dont do anything you haven’t practiced, ironed out the bugs and mastered, in that aeroplane, with that instrument setup, in VFR. If you have practiced both then you have given yourself the option.
I have done both but always prefer the stabalised approach in my first attempt (its safer and easier and I’m lazy) . If I dont get in off the approach, I then quickly assess the weather and work out if I can get in using the early descent to MDA method. If it is completely socked in, or I get in off my first attempt, the whole discussion is mute. I am then only thinking of attempting the early descent to MDA method for my second approach, having already flown the whole approach once and knowing the exact weather conditions.
Having an autopilot is invaluable in the early descent method as it lowers your flying workload at MDA and gives you more ‘headspace’ at this critical time to look out the window and assess the situation.

bob mcdonald May 28, 2010 at 5:32 pm

Come on guys, GPS is a wonderful thing with it’s LPV approaches, advisory glide slopes and the additional, unbelievable added situational awareness it affords us. Both techniques are valid when used appropriately. First of all, a well trained intelligent pilot does not dive the airplane to MDA,(I know it’s just a figure of speech)but it’s simply a stabilized increased rate, whether it be @ 500′/min or 850′/min. Lead the bloody level level off with the appropriate pitch/power inputs, stabilize with a bit of trim and fly the airplane! Real world flying is flying with the ability to constantly adapt to a fluid, constantly changing environment.

Jack Culley May 28, 2010 at 1:04 pm

1. Those advocating “dive & drive” must believe the same for an ILS….dive to the localizer only minimum. Isn’t the logic the same?

2. Dive & drive must result in more than 1,000ft/min descent. Used to be a sure way to bust a Part 135 check ride (in the 90′s) to exceed this rate. Standard derived, I think, from loss of a NWA commuter landing at Hibbing, Minn. on a LocBC using a “dive and drive” procedure.

3. Since WAAS I’m still in awe with the GS on GPS….can’t understand why anybody wouldn’t use it just like they do on an ILS.

Doug Rodrigues May 28, 2010 at 12:44 pm

There shouldn’t be any rule set in concrete. Depends on the terrain, the overcast, the visibility and if there are any tall towers around in the event you happen to lose track of your descent altitude. It can happen.

James May 28, 2010 at 11:43 am

Most of the operators I fly with are now preaching the stabilised appraoch, as if it is god-given. Remember folks, that in a DH situation, you make your decision at this height and per definition, WILL pass the altitude during a missed approach.

A MDA is a MINIMUM, so if you make this stabilised approach, you have to add a buffer to the MDA, as if you are in a descent at MDA, your missed approach will bust the MDA. So these operators add at least 50 feet to the MDA. Well, then if things are really tight, the earlier descent to the MDA and level flight to the MaPt could be the difference of making the landing or not. I have in response to this been told that, if the weather is that marginal that 50 feet make a difference, go elsewhere. Well, that may be valid, however, if another technique, gets you safely down without busting the MDA, why not use it?

Fly safe and still have fun!

James

Roger Hanson May 28, 2010 at 10:56 am

Most of the time I would favor the stabilized approach concept for the reasons stated – BUT – there is a time and a place for both techniques. Any pilot (let alone a professional pilot flying daily) benefits from being flexible and shifting strategy in accordance with changing conditions.

Here in the micro-climatology of the Pacific Northwest, there often are situations when the destination airport has that umbrella of hanging cloud cover directly overhead, which gives distinct advantage to an earlier descent to MDA (I don’t like the term “dive and drive”. Makes it sound like some thrill-seeker stunt – which it isn’t).

One element that comes to mind, and one I frequently deal with in pilot training and checking is the non-precision approach where a circling maneuver will quite likely be utilized. The “longer perspective” enabled by the earlier descent is a helpful aid in keeping the aircraft in a solid, safe position relative to the touchdown zone during that maneuver. “Solid and safe” provided the proper elements of the circling procedure are adhered to of course.

That said, I generally recommend during training and checking that pilots make good use of the stabilized approach advantage – and use the gift of advisory glideslope the GPS approach may give – unless, for the reasons outlined above, there may be a more effective strategy. It’s another thing to ponder during preflight planning and approach preparation.

Tim Daugherty May 28, 2010 at 10:54 am

It’s important to know and be proficient in both methods: the continiously stabilized approach is the safest and easiest method. There are at least two pitfalls to the “dive & drive” method: First, it’s far easier to inadvertently descent below the MDA. Second, it’s not the easiest thing to fly level at the MDA in conditions that aren’t quite VFR or IFR. If it’s really that marginal, pick an alternate with an ILS or vertically giuded GPS approach, shoot ONE non-precision approach – if you make it, fine, if not, go to the alternate! Give yourself the tools to make the trip a success and do so in the safest possible way!

George May 28, 2010 at 10:19 am

My instrument flying is somewhat dated, pre-GPS. However, in the east where I flew There were a lot of non-precision approaches. Having preformed the dive and drive technique frequently I felt that it provided a quick easy way to the runway. In retrospect thinking of younger instrument pilots it does open the door to a lot of flight control changes at a critical point in the approach. Making a glideslope like approach allows minimal power adjustments to go around or continue the landing. I agree it is the better approach under most circumstances. I enjoyed the discussion.

Bill Meeker May 28, 2010 at 9:35 am

I’m in the ‘get down fairly soon’ camp. With the 80-90 knot approach speed aircraft I fly, 750 fpm is more than enough to get me down to the MDA, level off, trim and track as best I can while scanning for the runway environment. Since we’re dealing with a non-precision approach where in some cases the runway I’m looking for is not as close to the middle of the windscreen as one might like, I’m OK with being underneath the advisory glide slope in a stable level flight condition while searching for the pavement/landing zone. Every non-precision approach is flown the same in this regard. I do advocate keeping track of where the advisory glide path is relative to my current position so I can anticipate where the end of the runway might be, ie underneath the glare shield. I’d be OK with a student using the other technique as long as they were consistent and could articulate the advantages/disadvantages of each approach, so to speak.

DaveS May 28, 2010 at 8:29 am

Dive and drive may well get you to the MDA outside of the visibility range to the runway, even with clear air under the crud, to no little advantage since a non-precision runway doesn’t always contrast well with its environment. But it always increases the opportunity to rid the world of a cellular tower or whatnot by consciously or otherwise flying the cloud base height rather than the MDA. Face it, guys, if you can see the runway at 1 or 2 Nm at the MDA there is little advantage in seeing it at 5 Nm, more risk, and in some environments, more public pressure over low-flying airplanes in cruddy weather.

John Collins May 28, 2010 at 7:51 am

Wally,

I am in the camp of keeping both techniques in the tool box. The way you described starting out at 750 ft per minute and reducing your descent rate as you approached the MDA / VDP is not a stabilized approach and won’t follow the advisory glidepath. For me, when the visibility is good, following an advisory glidepath using a stabilized approach is preferred. However, even in this situation, it may take some time at the MDA before you acquire the runway. Teaching the approach with an advisory Glidepath is the same as an ILS is wrong in my opinion. Unlike an approach with a DA where you make your decision at the DA and therefore momentum can carry you below the DA before the missed approach climb is initiated, you must level off at the MDA and not descend below it until the 91.175 cues are satisfied.

Flying the level MDA segment buys the pilot time when the bases are ragged or when the runway is difficult to find, with or without low visibility. Remember, the non precision approach runway often doesn’t have approach lighting. Since many of our GA aircraft can easily fly a 6 degree descent, one should not be limited to descending only at the VDP. Using a dive and drive approach to get to the MDA before the VDP provides the pilot more time to stabilize at the MDA and to search for the runway. In Christian’s post he gave an excellent example where visibility wasn’t an issue, but locating the runway was.

In my opinion you should teach both and being below the advisory glidepath should not be considered bad practice when using a dive and drive approach technique. Although the step down fixes are supposed to be below an advisory glidepath, the only policy I recommend is that the altitude at the step down fixes are the pilot responsibility and they should “Trust but Verify”.

FBFlyAgent May 28, 2010 at 7:48 am

Wally,

I believe and teach it similar to you. Though there’s little math in the cockpit, I look at my ground speed on the approach, cut it in half and add a zero to get the rate of descent I plan to fly from FAF to MDA @ MAP. It usually provides a 3 degree descent slope which is much more stable and safer than dive and drive. Dive and drive has gotten enough people killed to be disqualified as a useful technique on a non precision approach.

JT May 28, 2010 at 5:47 am

An advisory glideslope is just that — advisory. Headwinds or tailwinds may be evident in a GPS-navigation environment, but that will still require adjustments to the stabilized approach away from the norm. Given that, the stabilization argument is, to me, a wash.

So the answer that comes to my mind is “it depends.” The problem with not teaching your students both approach techniques is that they won’t have that other arrow in their quiver when they need it. And some approaches are much better done with a “drop and look” attitude. What the latest technology doesn’t teach is flexibility.

Even with GPS, there are approaches that will be much safer if you are allowed to visually pick up the airport before the MAP. If you’re teaching real-world instrument procedures (not the check-ride kind where you never see the airport before the MAP), stabilizing in level flight a mile or two before the MAP can make your flight safer and less stressful.

For instance, a VOR approach from the north to Hilo Airport (ITO/PHIT) on the Big Island of Hawaii leaves you in a fairly untenable position of you reach MDA at the MAP. Obeying the circling limitation of staying north of the airport requires a fairly steep turn to the right. Add a dark night with a low-wing airplane and you have a night circle in a 30-45 degree bank with visual references disappearing in a hurry. You’re two or three steps down the road to a seven-step accident progression that will invariably be classified as pilot error.

Short answer: What you teach depends on whether you’re teaching a pilot to pass a checkride or teaching him/her to fly instruments. My best instructors always taught me both.

Christian Kopp May 28, 2010 at 5:29 am

Hello together
Wally, I agree with you. Currently I´m an ATPL student, and my instructors do it just the
same way. But anyway, here in Germany most of the VOR or NDB approaches are made
in a way, that with descending on a 3degree track down to the MAPT you directly get there,
without levelling of. But, what in case you get of track, because of wind or something else.
Just had this in Augsburg (EDMA) on a NDB-DME approach down to rwy 25. We got nearly
1NM of track, because we had visual contact to the “rwy”, that was indeed a field,
covered with plastics, that looked like the rwy. !We! had visual contact, so the instructor
and me did the same mistake.
Ok this a visual failure, but in IMC you don´t have a chance to see the obstacles. So it
is indeed better, to make a flatter descend, to get to the VP directly, so there´s a greater
chance to get this safely on the ground. In my opinion NDB approaches, with only 1 NDB
near to field are the most challenging ones.
In case you have an ILS approach available, don´t lean to much on it. I had the “luck”
to catch on of those sidelobes of the localizer beam. And suddenly, nothing is reliable
anymore.
Happy flying, and always three green from Germany

Chris

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