Technique: Checkride versus reality

I had earlier instructed him to imagine that we had an emergency, such as an engine fire or smoke in the cabin. Instead of setting up an emergency descent, Michael followed the procedure for gliding after engine failure. I don’t know if it is a case of checkride jitters or lack of practice of a maneuver tucked near the back of the airman certification standards, but Michael is not alone. The emergency descent task seems not to get much attention in training, and the variety of creative techniques I’ve seen testify to that. Some candidates relate that they’ve done it just once or twice.

The emergency descent, as defined in the Airplane Flying Handbook, is a maneuver for descending as rapidly as possible to a lower altitude or to the ground for an emergency landing, within the structural limitations of the airplane. Multiple emergencies could require such an immediate and quick descent. For example, in the case of a cabin depressurization at high altitude, the goal is to drop to a lower altitude where cabin pressurization is no longer necessary. After that, a normal landing at an airport can be performed.

The descent technique is trickier if the emergency requires an immediate landing after the descent. An engine fire or smoke in the cabin typically requires a high descent rate as well as an expedited landing, possibly not at an airport. Additionally, a fire might compromise the aircraft structure, making the recommended technique sensitive to the total time spent in the descent and landing process. Higher airspeeds may help extinguish a fire but make it easier to compromise the structural integrity of the airplane and require more time to slow down for a safe landing. The energy with which an aircraft touches down involves the square of the groundspeed. For example, if an aircraft touches down at 50 knots instead of 70 knots, the energy that needs to be dissipated is half that of the faster aircraft. Roughly speaking, the survivability then doubles. Groundspeed on touchdown matters.

The FAA and aircraft manufacturer publications can make selecting an emergency descent technique confusing. For example, the airman certification standards for private and commercial airplane pilots require the candidate to establish and maintain airspeed and aircraft configuration for the emergency descent procedure recommended by the manufacturer. Interestingly, some aircraft manuals don’t publish a procedure, and if one is included, the reason for the descent often isn’t provided. A survey of approximately two dozen manuals showed that procedures vary widely, as can be seen in the four examples provided in “Sample of POH procedures,” this page. Additionally, the ACS requires a bank angle of 30 to 45 degrees in order to maintain positive load factors during the descent, but I never found a single operating manual that advocated banking the aircraft at all. If this sounds confusing, one might empathize with private and commercial candidates like Michael.

Emergency descent techniques generally involve placing the propeller in high rpm, reducing the manifold pressure to idle, and possibly pulling the mixture to idle cut-off. Faster airspeeds should be flown only in the clean configuration and with care. Banking should be done at or below the maneuvering speed (V_A) of the airplane (see “Proficiency: Not So Fast,” May 2019 AOPA Pilot). Gusts can impose loads that exceed the structural capabilities of the aircraft so it’s smart to limit airspeed to V_NO (or better yet V_A) if the air isn’t smooth. Generally speaking, increasing drag by extending the gear or lowering flaps can increase the descent rate but limit the airspeed (to V_LO/V_LE or V_FE, respectively).

It may not be obvious which technique will provide a safe and efficient descent in your own aircraft. To discern an optimal technique, first spend quality time with your operating manual to understand the possible limitations. Higher airspeeds might help extinguish a flame but are more likely to cause structural damage and those speeds need to be dissipated for a safe landing. Lower airspeeds result in reduced aircraft loads but they also limit descent rates. Slipping the aircraft can help improve visibility by directing smoke to the side but should be performed well below V_A as maneuvering speed does not protect the aircraft structure with extreme control inputs in two different axes.

To test profiles in your airplane, take along another pilot, ideally a flight instructor, who can assist in recording the data and provide an extra set of eyes on the gauges to ensure that you don’t exceed any operating limitations. Write out a test card in advance and let both pilots verify the aircraft is in the proper configuration before commencing a maneuver. Since the vertical speed indicator isn’t reliable for accurate descent rates, record the time t (in minutes) it takes to descend through a 1,000-foot altitude block. The descent rate is then 1,000 divided by t. I tested a Cessna 152 Aerobat and a Beechcraft Bonanza to generate procedures for my own aircraft (see “Exploring Various Procedures,” below).

I must say that the emergency descent procedure for the Cirrus SR20 and SR22 caught my attention. Risks of exceeding V_NE include parts leaving the airplane and aerodynamic flutter that may cause catastrophic structural failure. Personally, taking any airplane to V_NE would require me to get my courage up in a way that is incompatible with aviating. But I had to know more, so I turned to Cirrus aficionado Max Trescott for his take on the procedure. He was kind enough to make a video (youtu.be/fp3s-VOm3IQ) that demonstrates that a power-off dive in the SR20 at V_NO provides a 4,000 fpm descent rate—and I can only imagine the eye-watering descent rate that V_NE must produce. If you own such a model, I do not advocate testing the POH procedure and consider using it only during an emergency in smooth air.

I’m a fan of making my own aircraft checklists as the process makes me read my operating manual with a critical eye. While the likelihood of needing such a maneuver is remote, waiting for a true emergency to consult your checklist would be a mistake. Find and include the procedure(s) you deem best in your own emergency checklist.

Catherine Cavagnaro is an aerobatics instructor (aceaerobaticschool.com) and professor of mathematics at Sewanee: The University of the South.

Exploring various procedures

I used my own airplanes to explore various emergency descent techniques. Included are the published procedure and the flight test data. A video detailing this experiment can be found at aceaerobaticschool.com/videos.

Cessna 152 Aerobat (CE–A152)

POH: The handbook for the Cessna listed no procedure but recommended an airspeed of 85 knots (VFE but no mention of flap use is made). This profile resulted in a descent rate of about 1,000 fpm.