Thrust asymmetry
 

Hi,

I read somewhere that using NW steering is not efficient in case of thrust asymmetry after engine failure especially after certain speed and below Vmcg.

a) Is the statement above true?

Other persons mentioned the use of differential braking in case of thrust asymmetry after engine failure.

b) What is the recommended procedure by aircraft manufacturers (Boeing, Airbus, Bombardier...etc.) and/ or airlines/aircraft operators in case of thrust asymmetry after engine failure?

c) Is it possible/not possible to use voluntary thrust asymmetry in flight? Why it is possible/not possible?

d) What are the cases where it is possible (assuming it is possible) to use voluntary thrust asymmetry in flight?

Please explain your answer (please don't answer by only yes or no).

Feedback appreciated.

I've often used thrust asymmetry in BN2 Islanders while landing in very strong crosswinds in the Shetlands. When aligning with the runway I couldn't yaw the aircraft fast enough using rudder alone before drifting downwind .

HUH?
 

if you are taking off and one engine quits below vmcg or v1 you close the other throttle and now you are symmetric or pretty close to it.

I'm not really sure what you are getting at...and V1 is above Vmcg isn't it?

and in flight...use of asymmetric thrust is usually reserved for special problems like control problems

however, one can use asymmetric thrust in crosswind landings, allowing you a reserve of rudder...however again, you better know what you are doing if you are trying it for the first time with passengers aboard. certification is usually done with flight controls for x wind

AeroTech
What you are refrring to is known as low speed reject. If it happens with live engine at TOGA(Max thrust) it becomes more challenging as the yaw towards the dead engine is very rapid. Use of Nosewheel steering at high speed causes it to skid on wet runway and may be very viscious on dry so it is not recommended till taxi speed is reached. The correct procedure is to bring both thrust levers to idle, that removes the cause of the yaw and use both thrust reversers, the live engine acts as differential brake. If this not sufficient differential braking can be used on the live engine. It is very important to have adjusted the rudder peddles properly so that your foot can apply full differential braking. Runway excursion has happened due to improper adjustment. Inflight use of asymetric thrust can be done but is not a normal occurrence.

Thank you for your feedback.

I agree that closing the throttle(s) will reduce the asymmetry, but I think it will not bring back the airplane to the centerline of the runway especially if an outboard engine fails (if it is quad). There is a need for a force or moment in order to re-align the aircraft with the centerline of the runway (this is just my opinion)
Is there a risk of runway excursion even though the throttle(s) in twin/quad are closed after engine failure ? (based on your experience: sim or real engine failure)

Vilas,
Villas, I am wondering if the procedure you mentioned is aircraft manufacturer or airline/aircraft operator procedure?

According to my understanding of your posts, it seems that using thrust asymmetry in flight is not normal procedure. But it can be used when needed (crosswind landing, control issues).

Feedback appreciated.

Yes. If you're at slow speed on a surface with a low braking coefficient and suffer an engine failure with rapid thrust decay. Practiced this a few times in the sim but luckily not for real.

Even pre-briefed as a training exercise, we ended up fairly sideways but still on the runway. Made my list of "things to think about" before taking off.

You're probably at the most vulnerable just as the engines reach T/O thrust, which will likely be full power if there's contamination causing the lack of braking action. Chopping the other engine(s) in a timely manner appears to be key, otherwise an exit stage left/right is on the cards. Reverse deployment helps and you can attempt differential braking but if it's really slippery, that's not going to do much.

AeroTech
Sorry I missed out on applying full appropriate rudder as the thrust levers are simultaneously brought to idle which is very important because rudders are connected to nosewheel though with limited authority, and then apply differential braking if required. This is manufacturer's procedure.
Differential thrust is not used for crosswind. Generally any asymetry is trimmed off. I am not aware of any differential thrust usage.

Not generally true. Many airplanes have nosewheel steering that has no connection at all to the rudder pedals.

Not true. I use differential thrust all the time in landing in strong crosswinds. Also departing icy runways in a strong crosswind. Been known to use it on the ground when I've found my nosewheel sliding along on ice and snow.

A Squared
What I have mentioned is in connection with A320. Also it is equaly applicable to A300B4, A310, B 747 300, 400 series and most commercial jets. Differntial thrust on takeoff means you do not use TO thrust on one engine this will compromise your takeoff performance. I am not aware of this practice on commercial airliner. What I have quoted is from Airbus.

I must have missed the part where it was stated that these questions were exclusively about the A320. Could you point that out for me?


Actually on two engines, but only until you have sufficient airspeed to maintain directional control with with flight controls, then it's takeoff power on all 4.

Do you get a lot of icy runways in Malaysia?

Are you aware that there are other airplane manufacturers?

A Squared
I do not know which aircraft you fly. But on the jets I mentioned if takeoff thrust is not set on both engines by 8okts you cannot continue the takeoff. Also it will be nice if you quote your flight manual in support of what you do. Ice or no ice atleast the big jets have laid down contaminated runway operations that tell you if you can go and what you will do. No personal practices are allowed. I have flown the aircrafts I mentioned so I am experienced with two of the biggest manufacturers.

L382 Currently. It's in my Profile

Takeoff power would be set on all 4 engines well before that.

My Company manuals note that asymmetric thrust on takeoff may be necessary in some situations. It would only be those situations where the combination of wind and slippery runway surface kept you from maintaining runway alignment by nosewheel steering alone. Yes, I have encountered those conditions.

You're kind of missing the bigger point here. Some questions of a general nature were asked, where no specific operation or aircraft was stated. You're giving answers which are specific to your aircraft and operation as if they were absolutes. They're not.

A squared
b) What is the recommended procedure by aircraft manufacturers (Boeing, Airbus, Bombardier...etc.) and/ or airlines/aircraft operators in case of thrust asymmetry after engine failure?
This is not of general nature but type specific So I gave him Airbus procedure. I missed out A320. You gave your procedurecbut you also didn't mention the aircraft. We can't mix our procedures.

Anyone who refers to the Herk by its proper civilian moniker L-382 deserves my respect, regardless of what he's saying being accurate or not.

Thanks, I appreciate that, but are you implying that what I said is inaccurate?

Heaven forbid! I've never been closer than about 150 yards to a Herk, so I have no clue what the procedures thereon are. I can tell you I haven't used asymmetric thrust since my days of flying a Seminole, and even that was only for taxiing.

OK, no worries, just wasn't quite sure how to interpret that last bit.

I used to fly out of Ormond Beach many moons ago.

Happens to the best of us. I live down here, but never actually flew out of OMN. I've flown out of DAB as a pilot only once, nowadays I commute out of there to my base in ATL, where I currently sit as I write this.

;) Wasn't a bad place really. I was only down here during the winter months, Rest of the time in AK. Nice little bar in the flight school at he end of our Hangar row, and conveniently close to the Iron Horse for the Bike Week craziness.