Hello everybody,

I am sure most of you saw the pictures of the AF66 flight that had to divert, presumably as a result of an uncontained engine failure. Looking at the photos from this site (https://avherald.com/h?article=4af15205&opt=0), some questions came to my mind:

(1) Although investigation is not yet completed, from the pictures, it looks to me like the hollow shaft, driving the LP compressor and fan, broke shortly behind the mounted fan blades. It also looks like the fan hit the aircraft wing at a position that is located further away from the fuselage. Is this a lucky coincidence or are engines designed in a way that, if an uncontained engine failure happens as a result of a breaking shaft, the debris is ejected in a direction pointing away from the aircraft's fuselage? And if so, how is that design implemented?

(2) This is a question to the pilots on this board, who have experience on multi-engine aircraft: From this video of an A400M engine startup (https://www.youtube.com/watch?v=E7ZtXcTkEp0), I can tell that two respective engines are rotating in different directions, i.e. on both wings one engine is rotating clockwise and the other counter-clockwise. I assume this is the case for every multi-engine aircraft so that there is no net torque on the aircraft coming from the engines. Now if one engine has to be shut down during flight phase, there should be a torque, forcing the aircraft to enter a rolling motion. Assuming the aircraft is controlled manually by the pilot's inputs (i.e. no autoflight), does the pilot have to cancel/work against the torque, resulting from the engine loss? Or are modern aircraft systems intelligent enough to determine that torque and support the pilot, so that the control inputs a pilot has to make are the same, no matter if one engine is out or not? I am not talking about thrust here, I am only talking about the trajectory of the aircraft.

Please feel free to provide some professional answers, I am very much looking forward to that!

complementary rotation is limited to propeller propulsion.
In a jet engine the set of guide vanes behind the fan more or less "untorque" the departing airstream.
Then, it would be a major pita to produce mirror versions of any jet engines.
All aero ( turbine blades, guidevanes, .... ) surfaces would have to be produced in two version.
For turboprops the gearbox is changed ( like on the A400M) .
For Recip engines it is either gearbox or a ?different camshaft?

To me it looks like the fan disk itself disintegrated. Engines are not designed to contain or deflect any failure like that. They were just incredibly lucky that the debris did not hit the fuselage.
the fan case is wrapped in some layers of Kevlar that can contain a single fan blade... but not the whole fan.
I don't think parts of the fan hit the wing. We would probably see some holes and not just buckled skin panels. I assume the fan cowl or parts of the inlet cowl or fan case produced the damage we see at the leading edge.

Engine certification requires them to be tested for Fan blade containment at a specific rpm. Area surrounding the Fan blade have a Fan Blade Containment Ring for the same. However if a single blade is dislodged, adjoining blades also come apart due to the stress and the impact. This case it was just lucky it did not hit the fuselage.

Question 2: This A400M has got counterrotating Props on each side of wing. But if you notice other widebodies like 747,380 or even 340 for that matter all engines rotate in same direction. Reason being you have to change the Gearbox location and also the mass of rotation not being that great, it produces little Torque unlike a Helicopter Main rotor which has a large rotating mass. The PW GTF Engine has counterrotating spools in the engine itself i.e. Fan and N2 shaft rotate in one direction and N1 rotates in opposite direction

If you want to dig deeper into this you can refer P-Factor of Engines.

https://en.wikipedia.org/wiki/P-factor
Hope it clarifies your doubt.

The shaft broke, but at this time it's impossible to know if the shaft breaking was a primary factor or if it broke due to something else breaking and causing an unbalanced rotating load.

Rexus,

Answering your questions in order:

1) If there is an uncontained failure then there is nothing in the engine design that determines or limits the direction of debris.

There are multiple examples of uncontained failures where the debris ended up impacting the wings and fuselage, with two highlighted below:
http://aerossurance.com/safety-management/uncontained-cfm56-failure-b737/
http://aerossurance.com/safety-management/uncontained-cf6-aa-b767/
You'll notice the first is an uncontained fan blade-off event similar to the AF66 incident. The second is a high pressure turbine disc failure.
It's worth expanding on StereoTechnqiue's point that a single fan blade, or indeed a single compressor or turbine blade, should be contained by the casing. This is tested in engine design and there is a good video about it here:
https://www.youtube.com/watch?v=j973645y5AA
However, in the event you have a full fan disc failure, or turbine disc failure, the mass and energy of the assembly cannot reasonably be contained hence you get the failures you see here. Equally, with that amount of energy, there is not much you can do to direct the debris.

2) StereoTechnique and others are correct again that on jet aircraft with multiple spools/shafts the spools are counter-rotating so as to balance the torque during normal flight. As others have stated, this is primarily due to simplicity of design, manufacture and maintenance, otherwise you'd have to keep a spare left and right version of everything in stock! Therefore with one engine failed you don't get any particular effect of roll due to the loss of engine torque.
However, you will have a problem with asymmetric thrust. A shutdown engine, particularly one where the nice aerodynamic cowling has been removed, creates a lot of drag. When combined with the power the good engines are still generating this creates a large unequal force causing the aircraft to yaw. As the aircraft yaws the nose tends to disrupt flow to one wing which causes a slight loss of lift on that wing, hence you also end up rolling towards the failed engine. In most aircraft this would be countered through the use of rudder and ailerons to keep straight and level.
On an Airbus I think (any pilots to confirm) that with a single engine failure the aircraft remains in Normal Law and the aircraft will automatically trim the yaw and roll in the event of an engine out so that the pilot can just fly normally.

Hope that helps.

blista1989 wrote:

The second is a high pressure turbine disc failure.

I think this incident is pretty impressive. Especially this picture:



At first you might think the part just barely got contained... untill you realize this is the other engine and that the L/H engines turbine disk went through the fuselage before it got stuck in the R/H engines exhaust. You definitely don't want anything or anyone in the path of anything exiting an engine.


Source: http://www.dauntless-soft.com/PRODUCTS/ ... /AAEngine/

blista1989 wrote:

2) StereoTechnique and others are correct again that on jet aircraft with multiple spools/shafts the spools are counter-rotating so as to balance the torque during normal flight.

Applied counter rotation for N1 N2 (N3) spools is rather new actually.
first used afaik is the Harrier Jump Jet engine ( there to neutralize gyroscopic forces.)

Trent 900 is the first Trent with counter rotating HP spool.
GenX the first GE engine with counter rotating HP spool.

Horstroad wrote:

blista1989 wrote:

The second is a high pressure turbine disc failure.

I think this incident is pretty impressive. Especially this picture:



At first you might think the part just barely got contained... untill you realize this is the other engine and that the L/H engines turbine disk went through the fuselage before it got stuck in the R/H engines exhaust. You definitely don't want anything or anyone in the path of anything exiting an engine.


Source: http://www.dauntless-soft.com/PRODUCTS/ ... /AAEngine/

IIRC, in this particular incident (isn't this the AA 767 with the CF6 failure?) that piece of disk actually bounced off the tarmac UNDER the airplane before wedging where you see it ... in the OTHER ENGINE.

regarding AF066 ... you gotta wonder how much the fan housing absorbed before the whole thing ripped away.

Anyone have an idea if it could have sapped just enough energy off the disintegrating mess, to prevent really high velocity projectiles?

(it also helps that this stuff all spins much slower than the HPT turbine discs we've seen in other engine failures. Nothing stops those.)

litz wrote:

regarding AF066 ... you gotta wonder how much the fan housing absorbed before the whole thing ripped away.

Anyone have an idea if it could have sapped just enough energy off the disintegrating mess, to prevent really high velocity projectiles?

(it also helps that this stuff all spins much slower than the HPT turbine discs we've seen in other engine failures. Nothing stops those.)

It would have adsorbed very little energy, had it gone towards the fuselage it would have destroyed the airframe.
However the mechanics of this type of failure is that it comes forwards out of the engine and then downwards away from the aircraft.

blista1989 wrote:

2) StereoTechnique and others are correct again that on jet aircraft with multiple spools/shafts the spools are counter-rotating so as to balance the torque during normal flight. As others have stated, this is primarily due to simplicity of design, manufacture and maintenance, otherwise you'd have to keep a spare left and right version of everything in stock! Therefore with one engine failed you don't get any particular effect of roll due to the loss of engine torque.
However, you will have a problem with asymmetric thrust. A shutdown engine, particularly one where the nice aerodynamic cowling has been removed, creates a lot of drag. When combined with the power the good engines are still generating this creates a large unequal force causing the aircraft to yaw. As the aircraft yaws the nose tends to disrupt flow to one wing which causes a slight loss of lift on that wing, hence you also end up rolling towards the failed engine. In most aircraft this would be countered through the use of rudder and ailerons to keep straight and level.
On an Airbus I think (any pilots to confirm) that with a single engine failure the aircraft remains in Normal Law and the aircraft will automatically trim the yaw and roll in the event of an engine out so that the pilot can just fly normally.

Hope that helps.

In general, if it is a propeller aircraft, the torque effects in an engine out situation are significant and produce a rolling moment. This is most pronounced in light twins. Many light twins have engines rotating in the same direction, making one more "critical" than the other. Not only torque but asymmetric descending blade and propwash effects affect handling very differently depending on which engine you lose. In a turbofan this asymmetry is not nearly as significant to handling, if at all.

On an Airbus if you lose an engine you do indeed remain in Normal Law. The autopilot stays on. You can even autoland. On the 350 the autopilot is available even if both engines flame out.

Starlionblue wrote:

blista1989 wrote:

2) StereoTechnique and others are correct again that on jet aircraft with multiple spools/shafts the spools are counter-rotating so as to balance the torque during normal flight. As others have stated, this is primarily due to simplicity of design, manufacture and maintenance, otherwise you'd have to keep a spare left and right version of everything in stock! Therefore with one engine failed you don't get any particular effect of roll due to the loss of engine torque.
However, you will have a problem with asymmetric thrust. A shutdown engine, particularly one where the nice aerodynamic cowling has been removed, creates a lot of drag. When combined with the power the good engines are still generating this creates a large unequal force causing the aircraft to yaw. As the aircraft yaws the nose tends to disrupt flow to one wing which causes a slight loss of lift on that wing, hence you also end up rolling towards the failed engine. In most aircraft this would be countered through the use of rudder and ailerons to keep straight and level.
On an Airbus I think (any pilots to confirm) that with a single engine failure the aircraft remains in Normal Law and the aircraft will automatically trim the yaw and roll in the event of an engine out so that the pilot can just fly normally.

Hope that helps.

In general, if it is a propeller aircraft, the torque effects in an engine out situation are significant and produce a rolling moment. This is most pronounced in light twins. Many light twins have engines rotating in the same direction, making one more "critical" than the other. Not only torque but asymmetric descending blade and propwash effects affect handling very differently depending on which engine you lose. In a turbofan this asymmetry is not nearly as significant to handling, if at all.

On an Airbus if you lose an engine you do indeed remain in Normal Law. The autopilot stays on. You can even autoland. On the 350 the autopilot is available even if both engines flame out.

Without hijacking the thread, would that mean the A350 could possibly fly itself on AP all the way to landing with no engine power (assuming some source of elec / hyd) ?

If so, incredible. Wonder how they tested that!

77west wrote:

Starlionblue wrote:

blista1989 wrote:

2) StereoTechnique and others are correct again that on jet aircraft with multiple spools/shafts the spools are counter-rotating so as to balance the torque during normal flight. As others have stated, this is primarily due to simplicity of design, manufacture and maintenance, otherwise you'd have to keep a spare left and right version of everything in stock! Therefore with one engine failed you don't get any particular effect of roll due to the loss of engine torque.
However, you will have a problem with asymmetric thrust. A shutdown engine, particularly one where the nice aerodynamic cowling has been removed, creates a lot of drag. When combined with the power the good engines are still generating this creates a large unequal force causing the aircraft to yaw. As the aircraft yaws the nose tends to disrupt flow to one wing which causes a slight loss of lift on that wing, hence you also end up rolling towards the failed engine. In most aircraft this would be countered through the use of rudder and ailerons to keep straight and level.
On an Airbus I think (any pilots to confirm) that with a single engine failure the aircraft remains in Normal Law and the aircraft will automatically trim the yaw and roll in the event of an engine out so that the pilot can just fly normally.

Hope that helps.

In general, if it is a propeller aircraft, the torque effects in an engine out situation are significant and produce a rolling moment. This is most pronounced in light twins. Many light twins have engines rotating in the same direction, making one more "critical" than the other. Not only torque but asymmetric descending blade and propwash effects affect handling very differently depending on which engine you lose. In a turbofan this asymmetry is not nearly as significant to handling, if at all.

On an Airbus if you lose an engine you do indeed remain in Normal Law. The autopilot stays on. You can even autoland. On the 350 the autopilot is available even if both engines flame out.

Without hijacking the thread, would that mean the A350 could possibly fly itself on AP all the way to landing with no engine power (assuming some source of elec / hyd) ?

If so, incredible. Wonder how they tested that!

You could fly it to the ground but I don't think you'd manage an autoland. How would you stay on the glideslope?

Electrics can be provided by the APU or worst case the RAT. If you lose both hydraulics the independent actuators still work.

Starlionblue wrote:

77west wrote:

Starlionblue wrote:

In general, if it is a propeller aircraft, the torque effects in an engine out situation are significant and produce a rolling moment. This is most pronounced in light twins. Many light twins have engines rotating in the same direction, making one more "critical" than the other. Not only torque but asymmetric descending blade and propwash effects affect handling very differently depending on which engine you lose. In a turbofan this asymmetry is not nearly as significant to handling, if at all.

On an Airbus if you lose an engine you do indeed remain in Normal Law. The autopilot stays on. You can even autoland. On the 350 the autopilot is available even if both engines flame out.

Without hijacking the thread, would that mean the A350 could possibly fly itself on AP all the way to landing with no engine power (assuming some source of elec / hyd) ?

If so, incredible. Wonder how they tested that!

You could fly it to the ground but I don't think you'd manage an autoland. How would you stay on the glideslope?

Electrics can be provided by the APU or worst case the RAT. If you lose both hydraulics the independent actuators still work.

It would have to intercept from above and fly an amended glideslope at a higher angle, assuming you arrive in GS range at a high enough altitude in the first place. Agreed, not going to maintain 3deg with no power. I assume the independent actuators still require some amount of electrical power to function.

77west wrote:

Starlionblue wrote:

77west wrote:

Without hijacking the thread, would that mean the A350 could possibly fly itself on AP all the way to landing with no engine power (assuming some source of elec / hyd) ?

If so, incredible. Wonder how they tested that!

You could fly it to the ground but I don't think you'd manage an autoland. How would you stay on the glideslope?

Electrics can be provided by the APU or worst case the RAT. If you lose both hydraulics the independent actuators still work.

It would have to intercept from above and fly an amended glideslope at a higher angle, assuming you arrive in GS range at a high enough altitude in the first place. Agreed, not going to maintain 3deg with no power. I assume the independent actuators still require some amount of electrical power to function.

I think you are correct. If nothing else you need some electrics for the signaling.

In the event of uncontained engine rotor failure certification regulations allow a 1 in 20 airframe loss.

PhilBy wrote:

In the event of uncontained engine rotor failure certification regulations allow a 1 in 20 airframe loss.

Do you have a source you can cite?

AC 20-128A establishes 1 in 20 as the threshold for acceptable risk of a catastrophic outcome for safety analysis of 1/3 disk uncontainment.

Not exactly what was said, but probably the source for the statement.