Few of us will never need a 180-degree turn back to a runway following a power failure. But, if you ever do, here is a trick for you to consider. Recently, a Beechcraft B36TC Bonanza was cleared for takeoff from Runway 10L at North Perry Airport (KHWO), located six miles southwest of Fort Lauderdale/Hollywood International Airport in Florida. After liftoff, the Bonanza suffered an engine failure. The pilot attempted a right 180-degree turn to the parallel runway to land on or near Runway 28L. This is often referred to as “the impossible turn” for a variety of factors. Unfortunately, during the maneuver, it struck a utility line (unconfirmed) and then an SUV on the road adjacent to the airport. It came to rest in a ball of fire against the airport’s chain-link fence with tragic results. Both occupants of the airplane and a passenger in the SUV perished.
Had the airplane been 100 feet higher, it might have overflown the chainlink fence and landed on the airport property, which is open land. Assuming he used best glide speed, how else might the pilot get that needed 100 feet? A nearby doorbell camera captured the moment of impact and showed the gear was retracted. The next question is, did
the pilot consider placing the constant speed prop in the “coarse” position to minimize its drag?
For single-engine airplanes with constant- speed props, there is the potential to extend the glide path (or decrease descent rate) after an engine failure by pulling the prop control all the way out to low RPM. The terms low RPM, coarse pitch, and high pitch are synonymous, just as are high RPM, fine pitch, and low pitch. I will use the terms low RPM and high RPM because they best describe what the propeller is doing.
An airplane propeller is an airfoil. It creates lift (thrust) in opposition to airplane drag. A propeller also has an angle of attack resulting from a relative wind that is a complex interaction between the forward speed of the airplane and the rotational speed or RPM of the prop. Constant-speed props are usually found in higher performance airplanes
because they have a wider operating speed range and operate as an airfoil “gear shift.”
Actual In-flight Experience
In my Mooney Ovation, I experimented and determined that in high RPM, my descent rate was 800 fpm. In low RPM, it was 570 fpm. By reducing the RPMs, piston compression drag was reduced, and gliding distance increased by 40 percent.
I found that a Cessna 182 with the prop at high RPM descends at 857 fpm (RPM 1250). At Low RPM, throttle at idle, 70 KIAS produced a descent rate of 625 fpm (RPM 990). The difference in additional glide range is 37 percent.
The contrast between the two aircraft is possibly that the Mooney is clean and has a bigger engine—so the compression drag is a higher percentage of total drag versus a Cessna 182.
Implications for instrument pilots in single-engine airplanes with a constant- speed prop:
- Engine failure after take-off or on final: Consider the risk/benefit in taking-off when the ceiling is less than 1000 feet. If the engine fails, there is little time to troubleshoot, so pull the prop control out.
- Engine failure in cruise flight: Once troubleshooting is done and there is no hope of reviving the engine, pull the prop control out. (Follow the POH guidance.)
- When practicing engine failures, do not add power until the prop control is pushed forward.
This could be a life-saving exercise to perform in the airplanes you fly.
The Prop Control
I have demonstrated and taught that if your engine fails and the prop is still spinning, pull the prop control full aft. But it’s disconcerting that this is not in the Cessna 182 POH. However, the Textron (Cessna) representatives told the owners that in an engine failure, the pilot should pull the prop control back. So, the operator faces a dilemma. They don’t want the liability of changing the factory checklists, but pulling the prop is what you should do. It’s probably a safe assumption that glide performance in the POH is based on high RPM. When using low RPM, one can be confident that performance is better than that.
High RPM glide is a worst-case scenario. If you plan for that, low RPM or stopped prop is going to be better, but the POH doesn’t tell us how much better. If you lose oil pressure, the prop is going to go flat pitch, so, for many engine failures, coarse pitch might not be available.
Cessna test pilots responding to a request from the Civil Air Patrol (following two accidents) stated that pulling the prop has minor effect. This is counter to the data that I have personally collected in a Mooney Ovation and Cessna 182. Perhaps we could argue what “minor” means.
Pilot’s Operating Handbooks
In the Mooney Ovation pulling the prop isn’t on the checklist, but in a note: “Greater glide distance can be attained by moving the propeller control full aft
In the Bonanza A36 it is in the checklist: “Maximum Glide Configuration: 4. Propeller—Pull for low RPM.”
Piper Arrow II, like the Mooney, places the information in a note. “At best gliding angle, with the engine windmilling, and the propeller control in full ‘decrease RPM,’ the aircraft will travel approximately 1.6 miles for each thousand feet of altitude.”
Piper Malibu has it in the checklist: “Propeller Control … Full decrease.”
The Cirrus SR22 has a constantspeed prop, but the single-lever power control offers no direct prop control. So nothing is mentioned.
As noted, the Cessna 182 and 206 handbooks are silent on the subject.
As seen from this small sample of POHs, terminology and where it is presented are different; mentioned as part of a checklist, in a note, or not at all.
The FAA has long discouraged pilots from even considering the impossible turn. Still, the desire may be overwhelming when a power failure occurs, and all you see out the windscreen are buildings and powerlines, or trees and rough terrain. But if there is a field in front of you, go for it, as the turn is a hazardous maneuver under these circumstances. But a part of the decision is actually made before you apply power. You should have some idea of the airport environment and your skills, practice, and forethought. If you consider it an impossible turn, then it is as far as you are concerned.