Episode 372 - Airbus Engine Failure on Takeoff

A place to post misc. feedback to individual eps.
Forum rules
We'd love to have you Reply to posts in this Forum, but please don't create new Topics here. One exception: If we haven't created a thread for a particular episode, feel free to get it started. For other subjects, I suggest creating new Topics in Virtual Hangar=>Other Topics. Thanks.
User avatar
jarheadpilot82
Posts: 73
Joined: Wed Nov 24, 2010 3:13 pm

Episode 372 - Airbus Engine Failure on Takeoff

Postby jarheadpilot82 » Wed Jan 14, 2015 12:12 pm

Gentlemen,

I was listening to Episode 372 and the discussion of the apparent loss of an engine on takeoff by the Airbus 330, and Dave made the following comments -

—————

”They (2 engine commercial jets) are designed to actually fly through that failure at V1. You get to Vr you are supposed to be rotating. V2, you start to clean it up and, you know, set it up for climb. Well, if you have an engine failure at or after V1, the procedure is - add power and fly through it."

—————

As an air line pilot for the past 26 years, may I add a little bit to the discussion? This is simply meant to explain a little deeper what Dave was trying to convey the listener. This is my bread and butter, so to speak, so hopefully I can add a little to the discussion without putting everyone to sleep. The definitions below come from The Aeronautical Information Manual as well as FAR 25.107.

V1 is defined as the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

What does all that really translate to in layman’s terms? V1 speed is the end of the stop decision, not the start. If you achieve V1 speed and have not already begun the abort, then the decision has been made - you continue the departure. To begin the abort AT OR ABOVE V1 is to risk damage to the aircraft or people. You either stay on the runway but burn up the brakes to be able to do so and potentially cause a fire, or you risk running off the end of the runway and damaging the aircraft and/or hurting people. The only thing that would change that decision would be if you believed the airplane to be unflyable, and then, of course, you would have to stay on the ground, abort, and suffer the consequences.

Vr is the rotation speed. It is the speed that allows you to rotate and raise the gear, but still accelerate so as to reach V2 before reaching a height of 35 feet above the takeoff surface (basically, the end of the runway). Rotate at a speed below Vr and you may not make V2 before the end of the runway. Rotate faster than Vr (delay the rotation and continue to accelerate on the runway) and you may not reach your 35 feet clearance by the end of the runway.

V2 is defined as the takeoff safety speed. Takeoff safety speed means a referenced airspeed obtained after lift-off at which the required one-engine-inoperative climb performance can be achieved. FWIW, that climb gradient for a 2-engine aircraft is 2.40%. In other words, by the time you reach 1 mile horizontally (5280 feet) past the end of the runway after losing an engine at or after the V1 speed, you have achieved a height above ground level of 126.72 feet. I would like A LOT more than that, but that is the minimum height the FAA says the airplane needs to be able to achieve.

Also, I think a better way to explain this is to say that at V1, you “continue” the takeoff. I think that to use the phrase “fly through” implies that you fly through something that is not good, you get out of it, and things get better. “Flying through” turbulence might be an example. With an engine failure at or above V1, NOTHING gets better until you safely land. Also, just to clarify, after the initial rotation on an engine failure, the only initial clean up is gear up. From the 35 foot altitude above the runway to what my company refers to as “clean up altitude” (1,000 feet AGL in our procedures), V2 is the target airspeed, then at the clean up altitude you accelerate and then retract the flaps to an appropriate setting. If you are flying any distance at all to a divert airport, you would retract flaps all the way and accelerate to a higher speed. If you are returning to the departure airport and are, essentially, remaining in the pattern, you retract the flaps to a setting for the speed you wish to fly in the pattern. In the case of my airplane, the 757 or 767, it is Flaps 5, and 180-190 knots in most cases.

I do not know what other air lines do, but my air line does extensive engineering work to obtain the performance numbers and typically we do derated thrust take offs. That may be a foreign concept for many GA pilots, but that is what we do. Why, you ask? There is so much power available and the runway is so long that we have a performance margin that is huge. We don’t need full power for that given takeoff. It saves the company money on the fuel we burn as well as the maintenance on the engines. Think about this - if you stomp on the gas at a green light in your car, you certainly can do it and go faster quicker, but it costs you money. Or you can accelerate slowly because you have plenty of level road in front of you (and nobody is racing you). That is similar to thinking this way about derated takeoffs. There is so much excess performance, that in many cases we "trick" the airplane by telling it that the the temperature is higher, and the engine therefore derates to a lower power setting. That is the simple explanation for a very complex set of computations done by Georgia Tech grads a lot smarter than me. So when Dave talks about pushing the throttles up, that is the scenario. We did a derated takeoff, lost an engine at or after V1, shoved the “thrust levers” all the way to get max power from the remaining engine, put in sufficient rudder to maintain centerline (remembering it takes even more rudder if you shoved the power up to full thrust) and then rotate at Vr. That’s all… ;)

Jeb, I would beg to differ just a bit with what you said about reacting to engine failures being "almost too easy". That pilot made it look that way. Yes, there is a huge rudder to counteract the thrust of the one good engine, but it still takes a very qualified pilot to make that rudder move. I can remember many times taking off in Europe in a 767ER headed westbound to the U.S. with a full cabin, full of cargo and full of gas on a summer day (the proverbial "high, hot, and heavy") and as we were rolling down the runway I was thinking, "if we lose an engine at V1, this is really gonna suck..."

We practice engine failures every time we go into the simulator, and I hope I never see an actual, but my hat is off to the crew of the Airbus 330 in this video.

I hope some of this is interesting to those of you that have not been involved in this area of aviation. Thanks for indulging me, and those of you that nodded off can wake up now. ;)
Semper Fi,

Terry Hand
Athens, GA

User avatar
cozy171bh
Posts: 148
Joined: Mon Jan 07, 2008 4:07 am
Location: Las Vegas, NV

Re: Episode 372 - Airbus Engine Failure on Takeoff

Postby cozy171bh » Sat Jan 17, 2015 3:47 am

As a fellow 757 driver, I have to complement you on your great post, Terry. Excellent description of the performance factors in the takeoff profile. Another way of looking at assumed temperature or derated thrust takeoffs is that we "reverse engineer" the math to ensure we have the performance for the environmental conditions and weight for that flight to achieve the FAA profile. If we are light and with favorable atmospheric conditions, we use only the thrust necessary to do the job for that runway and the obstructions in the takeoff path. The payback is longer engine life and increased reliability.

User avatar
Scofreyjet
Posts: 399
Joined: Wed Jan 23, 2008 11:13 pm
Location: Billerica, MA/KBED

Re: Episode 372 - Airbus Engine Failure on Takeoff

Postby Scofreyjet » Sat Jan 17, 2015 6:07 pm

Not to worry, Terry - we always appreciate this kind of thoughtful and detailed explanation!

That A330 video has been around for a while now, but no matter how many times I watch it, I marvel at the reaction time and control shown by this crew.
Jeff Ward
I love things with wings!
Scofreyjet on Twitter

User avatar
C5Guy
Posts: 37
Joined: Sun Dec 09, 2012 10:47 am
Location: Freehold, NJ (3N6 - Old Bridge)

Re: Episode 372 - Airbus Engine Failure on Takeoff

Postby C5Guy » Sun Jan 18, 2015 8:44 am

The B-777, which I fly, has a feature called Thrust Asymmetry Compensation (TAC). The TAC system continuously monitors thrust levels from each engine, and if they differ by more than 10%, it automatically adds rudder to minimize (not eliminate) yaw. Engine failures at V1 are far less demanding compared to other large jets I've flown. I've heard the TAC could have ability to keep the 777 completely coordinated, but the designers thought it a good idea to provide the pilots a little bit of feedback. The 777 is an amazing piece of machinery.

User avatar
cozy171bh
Posts: 148
Joined: Mon Jan 07, 2008 4:07 am
Location: Las Vegas, NV

Re: Episode 372 - Airbus Engine Failure on Takeoff

Postby cozy171bh » Wed Jan 28, 2015 11:54 pm

C5 Guy - The 777 is a marvelous machine. I hope my air carrier buys some one day. The DC-8 was a bit of a beast with a V1 cut on the number 4 followed by a V2 cut on the number 3! The "device" for responding to the yaw was the size 10 shoe pushed full forward. Other sizes also worked well - as long as one does not confuse the left from the right!

These newer machines have come a long way!


Return to “Episodes”

Who is online

Users browsing this forum: No registered users and 4 guests