Slam Dunks and ‘Hair on Fire’
Descents (for Fun or Emergency)
by Hank Canterbury
Last month I talked about techniques and procedures for descending at various rates in our Bonanzas and Barons without harming either the plane or the engine. Those techniques offer a range of settings that will develop very high descent rates for emergencies, such as when you’re on fire or when you want to drop a few thousand feet in a hurry.
The Pilot Operating Handbook [POH] Emergency Descent calls for power to idle, prop full forward, gear and flaps approach (if installed), and airspeed to 154 KIAS. If you’re on fire, this is desirable, but a small caution applies for extended use.
If this maximum setup is used for a prolonged time, it has been suggested it might lead to crankshaft counter-weight de-tuning. At this time, there is no data to support that hypothesis. But if you’re on fire, that’s probably not a concern: getting on the ground as fast as possible is what you need right now! Other than for an emergency, you can greatly reduce the likelihood by using less than full rpm and manifold pressure [MP] above idle.
This may seem like an extreme maneuver, but it’s really not. If you are uncomfortable with the maneuver in any way, please ask a qualified instructor to show you how non-threatening it really is. While the technique can produce a high descent rate, it is fully controllable. Bonanzas and Barons can descend quickly without excessive airspeed. If you don’t need to go down as rapidly, then, as discussed last month, use less pitch / more power to modulate your descent to fit the situation.
OK, let’s give it a shot. To descend quickly under full control and without exceeding any airplane limits, do this:
- Select 2,300 – 2,400 rpm, smoothly retard the throttle to 15 inches (bottom of green arc), put the landing gear down and push the nose down to accelerate to and hold the POH gear down limit Vle. (If you’re currently faster than POH gear limit, simply hold the pitch level a few seconds until airspeed decreases, then put the gear down and push over). Using a lower rpm and MP above idle should reduce concerns about de-turning counterweights, while still providing a very substantial descent rate.
- You must lower the nose about 18 degrees and hold it there. Trim the nose down to assist – or the increased speed will quickly bring the pitch back up. Adjust pitch as needed to maintain – but not exceed – gear down speed limit Vle. If you don’t increase the angle of descent, the rate of descent won’t be as dramatic. It is necessary to increase your angle of descent for maximum performance while keeping airspeed under control with a combination of pitch, drag and reduced power. If your plane has an approach flap detent, half-flaps may be deployed up to the same airspeed as the landing gear, which, in most models is 154 kts indicated airspeed [IAS]. This will increase the airframe drag so you can quickly descend more steeply and gain additional rate of descent.
You will be surprised how long it takes in the steep descent for the plane to reach gear down speed with all the drag out and power reduced!
Below are the results from a test flight I conducted. Notice the reduced airspeed and descent rate when full flaps are used. That’s because when full flaps are used, the airspeed limit is less; consequently, the rate is less because you’re not going downhill as fast, even though the angle is nearly the same. Throttle was idle, rpm 2700.
If you thought slipping was the fastest way down, the results above provide some hard evidence that it is not. There are certainly times when slipping works well and is the preferred choice to make corrections. Examples would be on a base or final leg. The point is, you have more options than you may have thought were available.
The combination of throttle at 15 to 17 inches, rpm 2,300 to 2,400, gear and approach flaps extended, accelerating to and holding max speed will yield about 4,000 to 4,500 feet per minute descent without exceeding any limits. At that rate, you won’t need to do it for very long!
Using this technique, you can handle any “slam dunk” from ATC and easily maintain control of airspeed. What most pilots don’t do is push the nose down to a steeper flight angle when they increase drag; therefore, they don’t get the sustained increase in rate of descent.
It may be a bit unusual to see lots of dirt in the windshield, but it is very easy to modulate or stop the descent when you are ready by simply raising the nose. You are not in a screaming, accelerating dive requiring a high-G pullout; you’re about same speed as cruise. Even from a high rate descent, it only requires about 300 feet or less to level off. Airspeed rapidly decreases as you raise the nose. When you are level, reset power and configuration for whatever your next phase of flight will be.
Another variation that will add a bit more drag is mentioned in the FAA publications. Roll into a medium to steep bank (45 to 60 degrees) and increase Gs on the plane. Although this is true, I think you’ll find it simpler to just smoothly push over.
Flying the aircraft like this is fun. Best of all, it provides flexible options to achieve higher performance all within limits and without anxiety or harm. Should the time come when you need to make a rapid descent, you’ll be glad you practiced it. Give it a try: it’s fun.
Fly Often – Train Regularly – Review & Practice More!
ATP, CFII SEL & MEI