Twin Proficiency: Feather it Slowly

Twin Proficiency: Feather it Slowly

Twin Proficiency: Feather it Slowly

Feather that propeller when you have an engine failure
Feather that propeller when you have an engine failure

I was observing the demonstration of a piston twin Flight Training Device, or “simulator,” at a major university, where I was a consultant in the development of an “ab initio” airline pilot training program. Flying the “sim” was a senior airline captain who was also a consultant on the project. While the captain was at cruise speed, descending in a left turn on vectors for an instrument approach intercept, the sim instructor caused the right engine to fail.
Initially, the captain noticed nothing. A failed engine on the outside of a turn will tend to reduce the angle of bank. The natural reaction is to simply add more aileron to maintain the turn. High speed makes the flight controls more effective, so it only takes a small input to offset undesired performance. So, the captain adjusted his rudder and aileron just a bit as he continued his descending turn. He had timed it so he reached his assigned heading and altitude at about the same time, so he leveled the wings, raised the nose and throttled both engines way back to slow down. He may have noticed when that the airplane wanted to roll to the right, into the dead engine, but if he did he simply adjusted his ailerons to keep the wings level. Airspeed decreased rapidly and he subconsciously compensated.
His near-idle power setting meant there was little asymmetric thrust and, therefore, little indication the right engine was dead. As the decelerating twin reached the target approach speed, the captain advanced the throttles to maintain speed in level flight. That’s when he noticed the indications of a dead engine. The increase in asymmetric thrust at power-up, combined with the reduced control authority at approach speed and the departure from his desired approach course, made it clear something was wrong.
The captain’s training kicked in; he pedaled the rudder to hold heading, and he slammed all six engine controls – throttles, propellers and mixtures – fully forward. Then, in one swift, continuous move, he reached over, grabbed the propeller control and hauled it into the feathered position…on the wrong engine.
Grab and feather
Feathering the working engine’s propeller isn’t that uncommon. I saw pilots do it a lot when I was a piston-twin simulator instructor. It was usually the confident pilots, the ones who flew very well and often, who made this terrible mistake. As soon as they detected an engine failure, they would blaze through the engine-out procedure, rising to the challenge and spring-loaded to quickly feather a propeller, as if to demonstrate just how great a pilot they are.
Almost always, the pilot feathered the left propeller when I presented a failure of the right engine, even after properly identifying and verbalizing failure of the correct engine. Because most piston twins have a critical engine on the left, multiengine instructors tend to favor “pulling” the left engine. This means, in almost all cases, when a pilot feathers, or zero-thrusts, it’s the left prop. The experience and muscle memory developed in training reinforces feathering the left propeller.
Caught on tape
Although engine-out procedures for turbopropeller airplanes differ from those in piston twins, this left-engine training bias may have been a factor in a very high-profile airline crash. TransAsia Flight 235 was an ATR 72-600, departing Taipei, Taiwan, on February 4, 2015 with 53 passengers and five crew for a domestic flight. Two minutes after takeoff, the crew reported an engine “flameout”, climbing to a maximum height of 1,500 feet before banking steeply left and descending. Dramatic dashboard camera images of the airplane rolling nearly inverted, before impacting a highway bridge with the left wing and crashing, received wide distribution.
Taiwan’s air crash investigative authority, the Aviation Safety Council (ASC), released a factual report on the crash on June 30. Investigators determined that…less than a minute after takeoff, once the plane had climbed 1,200 feet, a master warning sounded, and a display showed that there had been an engine flameout, or power failure, in engine 2 (the right engine). The captain responded by pulling back on the throttle – but on the other, working engine, shutting it off about 46 seconds after the other engine failed, causing the aircraft to stall. The mistake was not noticed until about two minutes later, when the pilot managed to restore some power to engine 1 (the left engine) but it was too late to avoid the crash.
The captain’s last recorded words were, “Wow, pulled back the wrong side throttle.”
The video shows what appears to be the transition from a wings-level, high angle-of-attack descent to a Vmc roll-like departure from controlled flight – the stall to which the report refers.
Avoiding the snatch-and-yank trap
When I had use of a realistically performing type-specific Flight Training Device, I demonstrated the need to be expeditious but methodical when dealing with an engine failure, and how, as long as you maintain airspeed and directional control, you have ample time to work your way through the “identify, verify, feather” process.
To make this clear, I’d brief the pilot receiving instruction (PRI) I would present an engine failure, and all I wanted him or her to do was to hold the nose on the horizon, keep the wings level, and apply rudder as needed to maintain heading. In the Beech piston twins, the gear up/flaps up attitude for Vyse with a windmilling propeller is about three degrees nose up, and zero sideslip occurs at two to three degrees bank into the good engine, with about 1/3 of a slip/skid ball displacement. Wings-level with the nose on the horizon is very close to this optimal attitude/bank combination, an easy target under the stress of an engine failure in flight.
With the pilot well-briefed on responsibility – nose on the horizon, maintain heading, and nothing more – I presented an engine failure and let the PRI do his/her thing. Done correctly, the airplane would remain under control in a 200-400 fpm descent. The airplane was not going to careen into a Vmc roll as long as the pilot held that attitude, and the rate of descent was less than a normal final approach, with plenty of control authority to flare.
In other words, hold pitch and heading with a flare just before impact, and the worst that will happen is a wings-level, controlled slide into the ground, for which the airplane structure is designed to protect its occupants. That’s a far better outcome than an out-of-control crash from addressing the wrong engine.
We repeated the exercise a few times, and then I’d tell the pilot to accomplish the entire engine-out checklist, quickly but unhurriedly, while holding attitude and heading. We did this at high altitude in situations where the engine would restart in response to checklist steps, like turning on a fuel boost pump, and when it would not restart, requiring feathering the propeller. We did failures right after gear retraction, so restart steps were bypassed to get the propeller feathered as soon as practical. In all cases, the pilot found an ability to methodically work through the actions of the Engine Failure in Flight checklist with plenty of time to confirm the correct propeller was being feathered.
Stop the turn
Another simulator exercise was to introduce engine failures while the airplane was in a turn. As I said earlier, if the engine opposite the turn fails, especially at cruise speed, it tends merely to decrease the bank angle. You may instinctively apply more control to maintain bank angle, and might not notice the failure until you roll out of the turn.
A failure on the same side as the turn (“inside engine”) will steepen the bank angle and cause the nose to pitch downward, but at high speed you still might instinctively apply control inputs and not recognize the situation until the end of your turn. If you do detect an engine failure while turning, the rudder input required to maintain the turn may make the “dead foot, dead engine” identification process less obvious, contributing to improper engine identification.
All of which suggests that you’re most likely to correctly identify a failed engine when holding a constant heading. In other words, be wary of control inputs required when you roll out of a turn, and if you suspect an engine problem while turning, pick a heading and hold it before continuing with the engine failure and feathering procedure.
Do the two-step
There’s one last thing you can do to avoid feathering the wrong propeller. Make “verify” in your “identify, verify, feather” procedure a two-step process. First, do what is universally taught – pull the suspected dead engine’s throttle aft and confirm there’s no change in control requirement needed to hold heading (this is why holding a constant heading while identifying and verifying a failed engine is so important). Then, do a second verification by grasping the dead engine’s propeller control and pulling it aft to the feather detent – but not beyond – without letting go of the control. If there’s still no change in control input needed to hold heading, you have the correct propeller knob; pull it into feather. If the heading changes or it takes more or less rudder to hold heading with this second verification, you have the wrong prop handle in your hand; move it forward and try the verification with the other propeller control.
More pilots than you’d think snatch the wrong propeller control into feather when dealing with an engine failure in flight. Often it’s the higher-time, more-confident pilots who make this mistake. It’s vital to make control inputs immediately to maintain control when an engine dies, but it’s critical to be methodical in identifying, verifying, and only then feathering the propeller.

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2 Comments

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    Ronald Hays August 4, 2015 at 8:17 pm

    One of the more understated, great features of the 95 Model Beech Baron is the intentional placement of the engines closer to the fuselage than any other production twin. This makes primary SEO almost a non- event, handled easily with only a moderate amount of trim. Loose the right engine and the result is almost Ho-hum. At that point it is very akin to flying an A 36.

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    Adil Saleem December 10, 2016 at 4:58 pm

    Your comments on ATR 42 crash in Pakistan in December 2016 may very pertinent. A report on Geo News TV on 10 December 2016 showed that the one Engine failed and was shut down by the pilot. However, the report went on to mention that the other Engine did not feather and went into reverse thus stalling the plane, so to speak. Having read your article, I am not sure what to make of this. Any clarity for a layman?

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