The original post discussed the need for instructors to be aware that a major (severe damage) engine failure in a light piston engine twin requires prompt action to feather the propeller before the rpm falls below a critical figure – nominally between 800 and 1000 rpm. The current mantra taught by the majority of flying schools correctly emphasis the need to correctly identify the defective engine before feathering its propeller.
One of the steps recommended is to slowly close the throttle of the suspected engine to confirm it is indeed the correct one to feather. A slow closure is normally effected since a fast inadvertent closure of the wrong (live) engine by a pilot could leave the aircraft with no power even for a few seconds. The resultant airspeed loss would be rapid.
Realistically, the throttle precautionary closure of the suspected failed engine serves no other purpose at that instant except to confirm that the original assessment of “dead leg – dead side” was correct. Some light twin POH recommend the confirmation by use of throttle while others do not mention the technique. While this technique at a safe altitude and plenty of airspeed is acceptable, it is another thing altogether at a low airspeed and low altitude such as the initial climb after lift off.
It was in the days of four engine aircraft powered with piston engines (e.g DC4 Skymasters , Super Constellations or the military Lancaster bomber), that the confirmation of which engine had failed, came into being. For example, if an outboard engine failed, the strong swing towards the dead engine was usually quite obvious through the universally accepted dead leg – dead side confirmation technique. If an inboard engine failed, the swing was less marked although it was still obvious that an engine had failed on one side.
A problem arose if an outboard engine suffered partial failure. In that case from the swing alone it could be easily mis-identified as a failure of an inboard engine although a glance at the engine power instruments would normally give an indication which engine was the problem. So the technique came into being with four-engine aircraft that once the failed engine side had been identified by the dead leg, dead side technique, a slow throttle closure was effected on the suspect engine to confirm which of the two engines on one side had failed. If there was no further yaw when the assumed dead engine was throttled back, then it was generally safe to assume the dead engine had been further identified.
Conversely if closing of the suspect dead engine produced a further really severe swing then both engines on the same side were now out and the pilot had misidentified which was the dead engine.
Even if the two engines on the same side (one of which was truly dead while the other was merely momentarily throttled back and therefore windmilling) were out of action but for different causes, a four engine aircraft usually had sufficient performance to cope for a short time until power was quickly restored to the live engine. But pull back the wrong engine throttle on a light twin with already marginal climb performance on initial climb after lift off, then things soon get out of hand.
The original post resulted in contributors expressing their opinions on light twin take off performance and that is a good thing. This is where Pprune comes into its own with the number of readers having their say while the majority observe and ponder who to believe. But it still boils down to the need to get a defective engine propeller feathered before airspeed loss becomes potentially fatal due to the insurmountable windmilling drag. Reducing the number of actions before feathering is often the key to a successful single engine climb out performance.
In the type of piston engine light twins under discussion and with an engine failure shortly after lift- off, there will invariably be a "dead man's gap" of about 5-10 seconds where the speed and configuration means the aircraft is in a no-man's land for a few seconds. This is not new. Early military aircraft such as the twin-jet Canberra bomber and Meteor fighter sometimes had a 30 knots or more between lift off speed and minimum control speed. In that situation there are so many variables that it is impossible to consider each one before making a decision to forced land straight ahead or attempt a climb out. Of the variables, pilot skill is one vital factor. That means intimate knowledge of the asymmetric performance of his aircraft.
Lack of published single engine performance information in some POH, means rate of climb on single engine may be difficult to quantify; especially if the pilot has never experienced the doubtful pleasure of a real engine failure at that point in the take off flight path. That is the beauty of simulators.
The gear up, flaps up mantra, can be a bit of a trap. If the aircraft type requires a set take off flap (rather than a flaps up take off), and an engine fails shortly after getting airborne and the pilot whips the flap lever to up as part of the gear up, flap up drills, the loss of lift could be serious and the aircraft could sink back into the ground (problem solved re decision to stop or continue
Most pilots would agree that unwanted drag after lift off should be reduced as soon as it is safe to do so. That includes retracting the landing gear once the aircraft has attained a positive rate of climb. That way acceleration towards blue line is quicker. On the other hand, some pilots on initial twin endorsements are advised by their instructors to consider deliberately delaying retraction of landing gear until they guesstimate it is no longer viable to safely land ahead on the remaining runway length (taking into account forward vision over the nose, day or night-time, wet or dry runway, head or tailwind component, pilot reaction time, and maybe no time for the flaps to reach full down if airborne abort).
Rarely are figures published to calculate with any accuracy how much runway is needed for such an airborne abort. Hence the reference to “guesstimate”. Assuming the pilot has been certified competent to operate in command, there is clearly a necessity to making a correct and prompt decision if an engine fails suddenly shortly after lift off in a light piston engine twin. Should he close the throttles and deliberately elect to crash land because he thinks the aircraft doesn't have the performance to climb on one engine? Or does he think he can get away with it as long as he cleans up the drag and that includes prompt feathering of the failed engine?
To summarise: If, immediately after lift off, there is the proverbial loud bang and severe vibration of a badly damaged engine, there should be no need to go through the complete flying school engine failure mantra of the example detailed in the opening post. After all, the mixture levers should already be full rich (or as needed depending on density altitude), the pitch levers should already be at full forward, the failed engine already identified by the subsequent yaw, and no pressing need to confirm which engine has gone by slowly closing its throttle. These are all time wasters at low altitude since the immediate problem is windmilling propeller drag which in some aircraft is greater than the drag caused by an extended landing gear.
The prime identification has already been confirmed by the pilot’s immediate action of preventing further yaw towards the dead engine. Hence dead leg – dead side. Where an engine failure has occurred within seconds after lift off, the pilot may not have the time or airspeed available to afford the luxury of slowly closing a throttle to confirm which engine has failed. The pilot must get it right first time.
Caution: The comments above are personal opinion only. .