Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
In two-engine aircraft with wing-mounted engines when one engine quits the aircraft will have a natural tendency to turn to the dead engine. So if you need to turn, it seems logical it should be easier to turn that way.
However in the discussion here is a comment:
By dinger on Monday, Aug 11th 2014 13:42Z:
SOP in a twin is NOT to turn in the direction of the failed engine. Right engine failed and they turned Right.
Is it really standard procedure, and if it is, what is the reason behind it?
The AvHerald comment is correct, you generally do not want to turn towards the dead engine. The aircraft will tend to turn (both yaw and bank) towards the dead engine due to asymmetric thrust, allowing it to do so at low speed will make it difficult to end the turn, possibly to the point where you lose control. If you turn away from the dead engine, you'll have a tougher time getting into the turn, but the live engine will help you get out of it. That said, attempting low altitude turns with an engine out seems like a bad idea, you should concentrate on going straight and maintaining optimum airspeed to make sure you get some altitude
There are a couple of mnemonics when dealing with engine failures, like "dead foot, dead engine" (determining which engine failed) and "raise the dead" (keep bank towards the live engine)
I can only speculate as to why they chose to go right, either they wanted to avoid the populated area, or they were already unable to control the turn. The high density altitude would certainly affect the OEI performance as well, perhaps luring them into losing airspeed below Vmc.
Disclaimer: I'm not multi engine rated, and have no first hand experience. This is just what I've read.
I was recently PIC of a twin Aztec, when I was on a single pilot IFR departure. At about 800 feet at gross weight, without warning there was a loud bang and the right engine quit.
I was able to make a wide left 270 tear drop turn into the good engine which was operating at full power.
My multi-engine training taught me the skills necessary to survive this failure. A turn in to the good engine is taught for a reason. Raise the dead...
This helps the rudder have the authority to over power the asymmetrical thrust of the good engine. I believe a turn into the dead engine may have resulted in loss of control, and death.
The main thing is DON'T PANIC... Fly the airplane...
The good Lord was in control as The aircraft was loaded at gross weight (5 passengers and baggage).
I was able to complete the turn and land safely opposite the direction of my departure.
The stall horn was chirping through out the shallow turn, but my airspeed was right at Vyse (blue line). We were NOT climbing. The cause of the failure has not yet been diagnosed.
A spin is an aerodynamic, stable maneuver where one wing stalls and the other continues flying. To practice this maneuver once, turn into the dead engine of a twin engine airplane, the spin will be textbook perfect and you'll be back on the ground very quickly.
At low altitude eg on climb out, airspeed is low, no accelerated airspeed from prop on side of dead engine, if you turn into dead engine, airspeed over that wing drops even more and it will readily stall hence spin! With ample speed and altitude there should be no problem with a gentle turn.
The reason is that Vmca is not a fixed value (despite the red line), and actually increases as you are banked more toward the inoperative engine. If you start from a position banked to the good engine, you will have more rudder authority if turning to the good engine.
This video does a good job of explaining this, and especially between 10-16 min shows why you want to maintain bank toward the good engine and it's effect on rudder use.
Remember that the red line speed is based on a very specific set of conditions.
That’s kind of an old wives tale. The truth is you can turn into the dead engine, if you do it right.
Most certified twins are pretty well behaved airplanes with a failed engine, except at low speeds and low altitudes. Since control authority is more diminished here, there is s much greater tendency of the roll and yaw moments from the asymmetric thrust loading on the airplane to cause a departure from controlled flight. You must be very careful when handling these airplanes in this regieme of flight and never attempt to apply power below the minimum control airspeed with a failed engine as this is a death sentence in a twin. That being said smooth easy maneuvering of a twin at or above minimum safe single engine speed will be just fine, regardless of whether you are turning into the dead engine or not.
One key to performing the turn correctly is to keep the turn coordinated with the ball moved approximately 1/2 out of the center marks - “uncage the ball” - in the direction of the good engine. This will ensure no sideslip in the turn.
As part of a multi engine checkride, examiners will fail the critical engine in a left hand traffic pattern, forcing the pilot to turn into the dead engine in order to return and land. Examiners will also test things like engine failures in steep turns for MEI checkrides as well.
This answer is based largely on a critique of this video:
The video is interesting but I think it contained some fundamental errors in theory if not result. From 8:54-9:12 the author is speaking as if sideslip is a result of side force. That's essentially an Aristotelian concept rather than a Newtonian one. Sideslip is not a result of sideforce-- turning is. Rather, sideslip is a result of not being pointed the same direction you are actually going. Therefore it's inaccurate to say that when you are banked, the weight vector has a component that causes sideslip in one direction, or opposes sideslip in the other direction.
(Btw this pertains to related discussion in the answer Could a plane be constructed to be fly in fixed-stick roll-stable circles? -- specifically the comment "From the point of view of the aircraft, lift is still acting in the plane of symmetry, but gravity does not and will cause it to sideslip.")
What's really going on in the twin-engine case is that the slip-skid ball reacts to all aerodynamic sideforce components (but NOT to the sideforce component contributed by gravity, because gravity accelerates the aircraft and ball together-- this can also be explained in another way involving "centrifugal force".) When one engine fails on a twin-engine aircraft, if you want to exactly center an imaginary yaw string at the nose for maximum streamlining, the ball cannot be fully centered, because the rudder is strongly deflected and creating some sideforce toward the dead engine. That's why you leave the ball deflected about half a width toward the good engine--because it streamlines the fuselage. And fundamentally the rudder, not the bank anlge, is the control what controls the position of the slip-skid ball.
The purpose of the banking toward the good engine is to stop the turn that would otherwise result (due to the rudder sideforce) when the ball is in the optimum position, NOT to influence the amount of sideslip that is present. Similarly it is incorrect to suggest the banking TOO FAR toward the good engine would slip the plane sideways through the air toward the GOOD engine and possibly stall the vertical tail as a result, as the author suggests from 9:25 through 9:28.
Now, granted, if we are simply using the ailerons as needed to establish and maintain a set bank angle, and using the rudder as needed to hold heading while flying at that bank angle, then FUNCTIONALLY things would end up working much as the author says. (Except that the possibility of stalling the tail due to "too much bank" seems far-fetched-- are we really contending that the pilot is applying so much rudder toward the good engine that a yaw string would be deflected extremely far toward the good engine, despite the thrust imbalance? I don't think this is the true purpose of the 5-degree bank limit cited in the video.) At any rate, if we are flying in this manner, attempting to control heading with rudder, then too much bank could indeed produce some slip toward the GOOD engine, and too little bank would produce some slip toward the bad engine, both as indicated by a yaw string on the nose (rather than by the slip-skid ball-- though they will both basically agree whenever we are talking about huge deflections.) And when you lose an engine, initially one your first concerns probably is to apply rudder as needed to minimize yaw rate, so you might end up applying the controls in just this way. But fundamentally, the bank angle is not causing or preventing sideslip. Rather, the rudder is -- along with the yaw torque from the one working engine. In the long run, the bank angle is controlling turn rate, not sideslip.
IF airspeed is sufficient to give sufficient rudder authority to maintain the correct position of the slip-ball-- displaced about half a ball-width toward the good engine, then there ought not be any problem with turns in either direction.
On the other hand if you are fighting for basic control over the aircraft and you are having trouble preventing the aircraft from yawing and rolling toward the bad engine even with a lot of rudder applied-- which likely means the ball is still displaced rather far toward the good engine-- then the last thing you would want to do is bank toward the bad engine. The additional turning tendency would exacerbate the difference in airspeed between the two wingtips and cause the aircraft to tend to roll toward the bad engine. Banking toward the good engine will have the opposite effect and help you prevent the aircraft from rolling toward the bad engine.
VMCA is a loss of control speed. I find it talked about here as if it has something to do with stall speed. This is not correct. Turning towards the dead engine is not a death sentence. Turning towards the dead engine does not cause the airplane to spin. The loss of control is rudder effectiveness. If you are turning with either engine inoperative and you are close to VMC I would ask,”Why are you even close to VMC?” If you are turning you should always maintain blue line or above. You should also, always be ready to reduce throttle on the good engine if you run out of rudder.
Also, in order for a spin to develop we have to fly below VMC, run out of rudder, not reduce bank, not reduce power. The spin actually occurs when the plane skids and blocks airflow to the wing with engine inoperative. That being said, do not try to lift your dead engine with ailerons when close to VMC. The down aileron causes more drag and skids the airplane causing it to block airflow to the wing with engine inoperative.
Twin engines aircraft are designed to be relatively manœuvrable after V1 at takeoff whether they loose an engine or not. This is possible because the engines are not much apart from the X axis.
On modern aircraft such as the B 777 the thrust asymmetry is automatically compensated with the rudder. Once compensation is in place left turn and right turn, irrespective of the failure side, are symmetrical provided the aircraft speed is above a minima we will explain below.
Considering the worst condition, we loose the engines at take off, the aircraft is designed to be able to keep a minimum rate of climb with a speed not less than V2+10. Further when the airplane flies with an engine inoperative, there are redundancies in the design of the rudder, ailerons, elevators, and flap settings, which allow for the pilot to still control and fly the airplane, but to be able to control the airplane symmetrically the pilot must get the aircraft to a critical, minimal, controllable speed that the control surfaces can generate enough forces and moments to control the airplane, this speed is called VMCA (on ground we refer to VMCG).
Sure above these speeds we have full maneuverability, but we must understand how important they are when mapping out a flight plan, to plan for the unfortunate scenario where an engine is inoperative. Starting on the ground, if an airplane is on a runway and an engine gives out early, the pilot may be able to stop the airplane in time before the end of the runway, however if this is not the case then the pilot must take-off to avoid crashing the airplane at the end of the runway. This window of decision making is shortened if the airplane is on a short runway. If the pilot determines that they must take-off, then the calculations for the VMCG will blend into the calculations for the VMCA. It is extremely important for a pilot to know the bridge between these two speeds. If these speeds are relatively close to one another, the flight plan will merge from the VMCG to the VMCA. On the other hand if there is a major gap between these speeds then the flight plan should take this into account and adjust for it accordingly. Therefore there is a need to know these speeds and especially for the ability to calculate these speeds prior to the event of an engine failure. The flight plan becomes even more complicated if when there are geographical limitations surrounding the specific airport. These limitations include no-fly zones or mountains. Being able to calculate the VMCA and subsequently turn speeds will allow for a flight plan that will not crash the airplane into the surrounding topology.
For more details about VMCG and VMCA calculations please refer to :
https://repository.asu.edu/attachments/176507/content/Hadder_asu_0010N_16518.pdf
