Dive and Drive: Fact or Fiction? Maybe Both?

By Rod Machado


I am a "dive and drive" denier. There, I said it and I'm not taking it back. The term "Dive and Drive" is used by some instructors in the pejorative sense. It's a pointy phrase that's released like a drawn arrow to target pilots who cross the FAF on a non-precision approach and supposedly "dive" to the MDA, eventually "driving" the airplane into solid soil in a fit of CFIT (Controlled Flight Into Terrain). The "dirty" deed apparently results from a pilot's inability to level off at the MDA or his inability to maintain his MDA should he be lucky enough to identify it in the first place. Good golly, even Steven King can spin fiction like this, especially when you consider that there's no actual "diving" or "driving" involved in the first place.

To counter the assumed danger of "diving and driving," many CFIIs (and the FAA) recommend that pilots fly a "calculated vertical descent to the MDA"  on non-precision approaches. The "calculated descent" supposedly allows a pilot to leave the FAF and arrive at the MDA at or near the VDP (vertical descent point) or its equivalent, from which a normal descent to landing can be made. At this point, the pilot is expected to treat the arrival altitude as a decision altitude (DA) and either continue his descent or execute a missed approach. For some folks, the "calculated descent" to MDA is a far safer method of flying non-precision approaches and preventing IFR accidents. In that sense, not flying IFR at all is also a far better way of preventing IFR accidents, isn’t it? Staying higher on approach and arriving at MDA near the VDP certainly reduces your exposure to CFIT between the FAF and the VDP. Big surprise, right? It also reduces your chances of landing legally under instrument conditions (I'll explain why, shortly). And landing under instrument conditions is the primary reason you earned the instrument rating in the first place, isn’t it?

Why does the anti "dive and drive" crowd believe that instrument rated pilots shouldn’t be trusted to descend directly to the MDA, level-off and hold altitude? After all, instrument pilots don't seem to have any trouble holding altitude during other portions of instrument flight, do they? Apparently, it's only when they reach the FAF, reduce power and make a direct descent to the MDA that they supposedly forget how to fly. 

After 45 years of flight instructing I've rarely encountered a proficient instrument rated pilot who accidentally descended through the MDA. Even if one did, he quickly regained altitude, perhaps inspired by the recollection of a large planetary object resting directly beneath the airplane. No, you don't need the theme song from JAWS playing over a headset to be reminded to level off at an MDA. This is what instrument training trains a pilot to do reflexively. No doubt, an instrument rated pilot will occasionally blast through the MDA on a direct descent and possibly crash as a result. This rare exception, however, shouldn't be the basis on which to create operational rules.

The fact is that descending directly to the MDA at a reasonable descent rate is not the primary reason for accidents on non-precision approaches. Instead, a pilot is more likely to have a non-precision approach accident (especially at night) because he descends from the MDA prematurely (too far out on final), resulting in CFIT.

As a "dive and drive" denier, I'd like you to consider this. I always make direct descents to the MDA on all non-precision approaches. Why? Because I have a better chance of legally landing under reduced visibility conditions by directly descending to the MDA in lieu of making a "constant rate descent to the MDA and treating my arrival altitude as a DA. Additionally:

  • A direct descent and level-off often gives me more time and opportunity to identify and evaluate whatever lighting (LIRL, HIRL, MIRL, VASIs) is available in the runway environment for landing. 
  • The direct descent and level-off provides a better opportunity to sight the PAPI light projection (should a PAPI exist) under reduced visibility conditions (see *PAPI note below).
  • My workload is reduced slightly when making a direct descent to the MDA than when making a constant rate descent to the VDP...and so on.

No doubt, the "constant rate descent to the MDA" crowd had good intentions. However, it seems to me that these folks are not looking closely at the assumptions on which their argument rests. For instance, the "constant rate descent to the MDA" argument is based on several of the following misconceptions:

MISCONCEPTION #1: NON PRECISION INSTRUMENT APPROACHES WERE DESIGNED TO BE FLOWN LIKE PRECISION APPROACHES (ILS OR APV)

Not at all true (read TERPS). The typical non-precision instrument approach was designed for a 300-400 foot/NM descent (straight-in approaches) inside the final approach fix (FAF). In most instances, the pilot will level off at the MDA and fly to the MAP (missed approach point). If executed well and upon meeting the requirements of FAR 91.175, the pilot will leave the MDA and make a normal landing. Based on the way non-precision approaches were designed, a 90 Kt. groundspeed translates to a 450-600 FPM descent rate to the MDA past the FAF. That's hardly a "dive," but is clearly a normal descent rate. Keep in mind that the FAA considers descent rates in excess of 1,000 fpm to be excessive...and that's for "jet-type" aircraft. Therefore, anything less than 1,000 fpm is certainly not excessive. (I typically use about 800 fpm at 90 knots IAS for my descents on these approaches.) Of course, we want to arrive at the MDA prior to the VDP (visual descent point), or arrive at a point from which a normal descent to landing can be made. This might require a slightly higher rate of descent but in no way approaches anything similar to "diving." So, to describe a direct descent to the MDA at the rates described above as "diving and driving" is either naive and/or intentionally misleading. 

MISCONCEPTION #2: USING A "CALCULATED DESCENT" FOR NON-PRECISION APPROACHES IS EASIER, SAFER AND MORE LIKELY TO GET YOU INTO AN AIRPORT UNDER LOW VISIBILITY CONDITIONS

Not necessarily true. First, calculating the rate of descent required past the FAF to the VDP (or a calculated VDP) based on your groundspeed prior to reaching the FAF is not easier for the IFR pilot. In fact, it increases the pilot's workload. After all, this is something you have to calculate based on whatever wind conditions exist just prior to flying the approach.

Second, this method requires pilots to maintain a constant rate descent in hopes of accurately arriving at the VDP (without any glidepath indication by which to ensure the intended outcome of that descent). Good luck with that. You are just as likely to overshoot as undershoot the VDP rather that arrive precisely at it when using VSI for vertical guidance without the aid of electronic glidepath information. 

Third, the reason pilots typically experience CFIT on an instrument approach isn't that they can't level off or hold altitude at the MDA. The reason for accidents in this category is that pilots typically leave the MDA at a point where a normal landing can't be made (typically done under the influence of the "black hole" visual illusion). Modifying the way an approach was designed to be flown just to prevent the pilot from being tempted to leave the MDA early doesn't say much about that pilot's training, much less about his ability to make reasonable in-flight decisions (but I do acknowledge that some pilots will not make reasonable decisions, nevertheless). So, if you really want to protect yourself on an instrument approach, don't even descend to the MDA, stay at the intermediate or initial approach segment altitude and overfly the airport at several thousand feet above the ground. Now that's protection, isn't it? It's also how you completely eliminate the utility of an instrument approach and your hard-earned instrument rating. Instrument pilots are (or should be) trained to descend to an MDA and fly to the MAP safely.  

Fourth, nearly all non-precision instrument approaches are flown without the use of an ALS (approach lighting system) unless these approaches are flown to a runway having an ILS approach. This means that pilots flying non-precision approaches typically use a VASI to help safely transition from the MDA to landing. If they are lucky they'll have a PAPI, which provides the highest intensity of horizontal illumination among the class of VASIs (as discussed in great detail in my IFR Handbook). The PAPI is seen best through restricted visibility phenomena at relatively "LOWER" altitudes—at MDA—not higher altitudes above the MDA (which is likely when making calculated descents to the MDA)*. That's why you want to be at the MDA long before reaching the VDP to help you identify, assess and utilize what little lighting might be available for a safe transition to landing.

(*Note: Consider, for instance, that PAPIs project a highly luminous light beam—on the order of 40,000 candelas during the day—with the maximum projection of this light occurring at an angle of 3 degrees above the horizontal. Of course, you can see the PAPI lights above and below this angle. However, you just can’t see them as well farther from the runway during night or daytime hours. (See graphic below.)

Fifth, some pilots argue that reaching the MDA and VDP at the same time allows them to treat the arrival altitude as a DA (decision altitude). These folks believe that flying a non-precision approach this way—similar to how an ILS is flown—provides them with ILS-like safety, including reduced CFIT potential. This is a mighty big assumption that's betrays a deep deep misunderstanding of how ILS approaches are constructed and flown. Please remember that a very important component of the ILS is the approach lighting system (ALS) which was designed primarily to help pilots "transition" for landing under very low visibility conditions at a very low altitude in close proximity to the runway threshold. The practical reason for descending directly to the MDA on a non-precision approach is to provide you with a better opportunity to "identify" the runway environment (LIRL, MIRL, HIRL, VASIs, etc.) as early as possible on final approach. This helps identify your position in relation to the runway's geometry (the runway's proximity and horizontal/vertical orientation to your airplane, and so on). This aids you in making a safe transition from MDA to landing when ILS approach lighting isn't available. Trying to make a quick decision about whether or not to continue your descent for landing at a "pseudo" decision altitude puts you at a tremendous disadvantage. Think about it. You have to make the same decision you’d make when flying an ILS approach without having the same lighted runway environment. Isn’t this why the largest mandatory increase in minimum flight visibility on an ILS occurs when the approach lighting system is inoperative? You bet it is. Therefore, treating your non-precision approach as if it’s an ILS-like procedure might prevent you from landing under low visibility conditions or, even worse, attempt a landing without a clear idea/understanding of the runway environment. Ultimately, it means getting less utility of your airplane and the instrument rating you spent a great deal of time and money earning.

MISCONCEPTION #3: GENERAL AVIATION AIRPLANES SHOULD BE FLOWN AS IF THEY ARE MODERN AIRLINERS SINCE AIRLINE PILOTS HAVE FEWER ACCIDENTS Good golly! I am always puzzled by why some pilots would believe the first part of that statement (despite the fact that the FAA clearly believes it). As I've said so many times before, there's almost nothing about flying a bigger airplane that pertains to flying a smaller airplane, but almost everything about flying a smaller airplane pertains to flying a bigger one." Granted, when airline pilots fly non-precision approaches they typically use some form of "electronically calculated or projected descent" to MDA. That's fine. They should fly the way their company wants them to fly. And, of course, airline pilots have fewer accidents, but let's remember why. Airline pilots don't fly alone, they don't fly without advanced equipment, they don't fly without a precise idea of what they're "supposed to do" in the cockpit, they are required to follow the strict dictates of FAR Part 121 which clearly wasn't written by a party planner, and, most important, they have thousands of hours of experience and have the opportunity to practice their flying skills to proficiency (to name just a few).

GA pilots are different. We can fly as safely as we want to fly because safety at the GA level is based on the choices we make, not the mythical fate that's said to hunt us. That means if pilots don't feel comfortable descending to an MDA and leveling off, then they shouldn't do it. If they are unable to resist the temptation to leave the MDA prematurely, then they shouldn't descend directly to the MDA (but I would question why they are flying IFR in the first place). If pilots feel that making a constant rate descent to the VDP causes them less workload and less stress, then they should fly using this procedure. So be it

When I was young my dad would try to reason with me by saying, "Hey, just because your friends jump off a bridge doesn't mean that you should jump off a bridge, too." Of course, that logic worked on me, at least until someone invented bungee jumping. So just because jet pilots (corporate, regional and airline) fly constant rate descents to landing on non-precision approaches in their bigger airplanes, doesn't mean you have to fly your smaller airplane like this. As I see it, there’s no practical reason for a trained instrument pilot not to fly an instrument approach the way it was originally designed to be flown. I only ask that those pilots who claim that descending directly to the MDA is, by its design, a dangerous "Dive and Drive" activity, rethink their position. 

Then again, your mileage may vary.

By Rod Machado | | Be a Safer Pilot, CFI Resource Center, PTS-ACS Arguments, Technique | 4 comments
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Comments

  • Ray - February 01, 2019

    Maybe I am just dumb or nobody told me l could but I always thought that there was a reason for anMDA like keep you out of the trees. There is rule In designing approaches related to feet above and how far out. I wonder what they thought they were doing.

  • Dennis Carew - February 01, 2019

    You’re right! More time to find the runway/airport in low visibilities. A controlled decent, flying by the numbers is not a wild steep dive, but a very accurately controlled stablized decent. Flying level at the MDA is a basic IFR skill. Basic aircraft control, positional awareness are skills all IFR pilots must maintain.

  • Harold - February 01, 2019

    Right on, Rod. I fly an RJ under 121 rules, and we do use the “derived MDA” procedures laid out in our OpsSpecs, but there is no reason to be training GA pilots to do the same. When I teach instrument student’s, I expect them to fly at the MDA until the MAP, with the understanding that there is a chance they will not be able to make a normal approach if they spot the airport after a published or derived/manually calculated VDP.

  • Carl - January 03, 2019

    Totally agree! My airline years ago started training for the constant vertical decent rate to MDA. I found it never worked out because of all the variables. The wind would change, corrections had to be made for high altitude airports with higher ground speeds for the same air speed and the mental gyrations doing the math while executing the approach. You would arrive at MDA either late or early. Additionally, a miss from level flight is much easier than from descending flight which has a chance of going below minimums prior to establishing a climb.

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