Moderators: richierich, ua900, PanAm_DC10, hOMSaR
Symmetrical thrust reverser deployment
I've heard of Lauda Air Flight 004. I know that the left engine reversed thrust in the air and that caused the plane to roll to the left and crash. But what if both of the engines on (say) an A350 or a 777 (or a 767, for that matter), reversed thrust simultaneously during flight? Would the plane just stall and land on its belly?
-
- Starlionblue
- Posts: 21730
- Joined:
Re: Symmetrical thrust reverser deployment
There have been, and still are, large jets which can reverse in flight. So it should be controllable.
There's really no need for a stall as long as airspeed is kept up by diving.
I think if you couldn't stow the reversers the best action would be to set the engine masters to "off". At least then you'd just have two large airbrakes instead of engines actively thrusting in the wrong direction.
Now the question is whether you can arrest the sink rate in a fashion that avoids hitting the ground too hard.
I'll add that this scenario is exceedingly unlikely. There are three separate locks on the reversers.
There's really no need for a stall as long as airspeed is kept up by diving.
I think if you couldn't stow the reversers the best action would be to set the engine masters to "off". At least then you'd just have two large airbrakes instead of engines actively thrusting in the wrong direction.
Now the question is whether you can arrest the sink rate in a fashion that avoids hitting the ground too hard.
I'll add that this scenario is exceedingly unlikely. There are three separate locks on the reversers.
Re: Symmetrical thrust reverser deployment
Like a few minutes after takeoff on an A3510 or a 773ER, and both thrust reversers deploy in flight, at the same time, and without being commanded. I think that the plane would just stall (because, again, too much of that turbulent "blast" created by the fast forward speed and the reverse thrust goes over the wings) and land on its belly.
-
- GalaxyFlyer
- Posts: 12400
- Joined:
Re: Symmetrical thrust reverser deployment
The C-5 could reverse the inboards in-flight, as there were not airbrakes. Coming off a training AAR mission, crew used the thrust reversers, but couldn’t stow them. Yes, they were temperamental. Instead of shutting down both and landing on two, very possible at their light weight; they left them running in the mistaken opinion that having the generators and hydraulics (both of which were powered with the inboards caged); the py diverted into LNK. When Lockheed was asked the next day, the engineers asked, “ where was the crash?” Turns out, if LNK were a few miles further, they’d have crashed. The descent and closeness of LNK meant they never found out the the best they could manage was a 800-1200fpm ROD.
GF
GF
-
- GalaxyFlyer
- Posts: 12400
- Joined:
Re: Symmetrical thrust reverser deployment
I bet that a B767/777 wouldn’t fly for long with both TRs deployed. My understanding from a Boeing propulsion engineer, lose of control is very rapid, so remaining upright would be luck. It wouldn’t land “on its belly”, more like rolling, upside down, nose low.
GF
GF
Re: Symmetrical thrust reverser deployment
The FADEC on many modern jets will command thrust to idle in the event of a reverser deployment in flight.
-
- GalaxyFlyer
- Posts: 12400
- Joined:
Re: Symmetrical thrust reverser deployment
Idle will still have a large effect on the flow over the wing, destroying lift. In my C-5 example, thrust was at idle and even at very light weight, level Flight was impossible.
GF
GF
Re: Symmetrical thrust reverser deployment
So it would stall, then pitch nose down, possibly going vertical and partially invert itself?
-
- GalaxyFlyer
- Posts: 12400
- Joined:
Re: Symmetrical thrust reverser deployment
If symmetrical, possibly. If asymmetric, begin uncontrollable roll, possible breakup shortly thereafter as in the Lauda crash.
GF
GF
Re: Symmetrical thrust reverser deployment
The reverser deployed and seperated from the aircraft while striking the horizontal stab, No one applied reverse thrust to the engine, The crew mistakenly thought the reverse light was a false warning. The PW powered 767 has hydraulic actuated reversers, where as the GE uses bleed air.
As others have noted some models of the DC8 were capble of inflight reverse to aid in descent. In addition the C17 has inflight revers trust, I think on the inboard engines only. I have watched videos of it being used and it's pretty rough.
As others have noted some models of the DC8 were capble of inflight reverse to aid in descent. In addition the C17 has inflight revers trust, I think on the inboard engines only. I have watched videos of it being used and it's pretty rough.
-
- Starlionblue
- Posts: 21730
- Joined:
Re: Symmetrical thrust reverser deployment
acjbbj wrote:So it would stall, then pitch nose down, possibly going vertical and partially invert itself?
That really depends on symmetry of deployment, control inputs and control logic.
For example assuming symmetrical deployment once airspeed reaches low speed protection, an Airbus in Normal Law would pitch down to maintain airspeed. However that scenario is predicated on the THS and elevators having enough control authority to overcome pitch moment from reverser deployment. Lots of variables.
I wonder if this has been modeled. Someone must have numbers...
Re: Symmetrical thrust reverser deployment
GalaxyFlyer wrote:If symmetrical, possibly. If asymmetric, begin uncontrollable roll, possible breakup shortly thereafter as in the Lauda crash.
GF
Depends on what aircraft you are looking at. The MD11 is capable of flying with one wing engine thrues revereser deployed. They proved this during demonstration flights. MD even claims the MD11 can land in that configuration.
So I guess the outcome of a symmetric thrust reverser deployment is also somewhat dependent on the aircraft and its characteristics.
Who is online
Users browsing this forum: A40-TY, Google Adsense [Bot] and 35 guests