Emergency descent: What’s your procedure?

By Donald Talleur

"Emergency descent" is a phrase that conjures up images of steep descent angles, high rates of speed, and sweaty palms. I am not sure why, but when I ask to see an emergency descent on a checkride, I usually get a glide with an engine failure troubleshoot procedure. The applicant is usually confused when, after making a successful approach to a field with their simulated "dead engine", I ask them to climb back up to altitude to show me an emergency descent. Of course I understand that the most common emergency that student’s practice is the engine failure emergency with subsequent glide to a simulated forced landing. That’s fine, but when the words emergency and descent are combined, we’re talking about an entirely different maneuver.

The emergency descent is a procedure designed to get you down and possibly on the ground quickly. You might have a fire, passenger problem, cabin decompression, weather problem or you may have the onset of pilot incapacitation. In any event, a fast descent is in order. The nature of the descent generally depends on the type of aircraft you’re flying. For instance, The Piper Seminole, a light twin-engine aircraft, makes it’s emergency descent well below Vne (velocity – "never exceed") and with the landing gear extended. A Cessna 414, on the other hand, makes the normal emergency descent near Vne with the landing gear retracted unless you’re descending in turbulent conditions. Then the manual recommends Va (velocity – "design manoeuvring") and gear down for the descent.

If you’re in a light single-engine aircraft there may or may not be a prescribed procedure. Generally, however, you can expect that any airspeed from Va up to Vne for descent will be required.

In lieu of prescribed procedures for the emergency descent what should a pilot do? Let’s address that question and hopefully you’ll go away with a procedure that is acceptable for your aircraft. First, if its an engine fire, extinguishing the fire is key and getting on the ground is critical. If you are at high altitude, an emergency descent is advisable. Airflow through the engine cowling can extinguish most types of engine fires. However, the speed is the critical factor in extinguishing the fire. If you are too slow, the fire may not go out! While the guidelines for determining the exact speed to put out an engine fire are vague, one point of agreement among manufacturers is that there is some speed that creates an incombustible mixture of fuel and air. This is generally at high speeds where there is too much air for the amount of fuel (or fuel source) or too much draft. Suffice to say that you can snuff out a fire by either having too much fuel for the amount of air or too much air for the amount of fuel.

The speed that you choose is clearly dictated by several factors: 1) the apparent magnitude of the problem at hand, 2) the altitude available for descent, and 3) familiarity with the aircraft. Given sufficient altitude and familiarity with the aircraft, a descent exceeding Va will probably be necessary to put out an engine fire.

At some point you must decelerate in order to make a forced landing. One of the biggest errors I see when observing emergency descents is the failure to make a timely transition to a safe speed for landing. Don’t create a bigger emergency than you already have by failing to plan for the landing. If your piloting skills and familiarity with the aircraft are questionable, then you may want to descend at a slower speed so you can get slowed in time for a landing. If altitude is not available for a high-speed descent, then consider circling over your current location for a landing. Remember that altitude lost while gliding will increase during banked turns so be careful when judging how many complete turns to make before rolling out to an approach to landing.

Retractable gear aircraft that do not prescribe a procedure for emergency descent require a little more forethought. The question here is whether to extend the gear and remain at or below Vle or to leave the gear retracted and use a higher airspeed. My personal preference is to extend the gear. This eliminates one extra thing to remember to do prior to landing. If altitude permits, however, I may leave the gear retracted and descend at a faster speed in order to put out the fire. The main issue is that you must plan the descent so you can get to the ground safely. That requires a deceleration below Vle (velocity – "maximum landing gear extended") at some point in order to extend the gear. If you prefer to descend gear up, make sure to plan for the slowdown so you don’t run out of altitude and ideas all at the same time. You should simulate both a gear down descent and gear up descent at higher speed. I think you’ll find that the drag created by the gear is sufficient to increase the rate of descent to the point where it closely matches a gear up descent at higher airspeeds.

Pilots should always follow the manufacturers’ recommendations, but even those can be modified if your particular situation dictates. Practice these procedures with a qualified instructor and determine which procedure you will use in the event of a real emergency. Always plan carefully for even the remotest of emergencies. These are the ones that will catch you of your guard!