16
$\begingroup$

I play a flight-sim called X Plane. The other day while I was approaching an airport a little too fast and knew I couldn't slow down in time. I decided to use the reverse thrust while I was still in the air and this helped dramatically and I was able to land safely.

But now I'm curious - Would using reverse thrust in a real-life Boeing 747 have the same effect, would it cause the plane to crash, or go out of control?

|improve this question
$\endgroup$
  • 1
    $\begingroup$ This was the first thing to come to my mind. It could stall the airplane near the ground, resulting in a crash. youtube.com/watch?v=WKCl3lfAx1Q#t=132 $\endgroup$ – Keegan Nov 10 '14 at 20:06
  • 3
    $\begingroup$ Flying with reverse thrust reminds me of this: youtube.com/watch?v=6YkkZw9GVaU $\endgroup$ – slebetman Nov 11 '14 at 2:58
  • 2
    $\begingroup$ The space shuttle had such a low L/D profile that it was simulated by a jet flying with the thrust reversers deployed. en.wikipedia.org/wiki/Shuttle_Training_Aircraft $\endgroup$ – BowlOfRed Nov 11 '14 at 6:33
  • $\begingroup$ This might be interesting to take a look at: youtube.com/watch?v=Yq5HLtdGeqE $\endgroup$ – Alexander Johansen Nov 11 '14 at 14:03
  • 1
    $\begingroup$ Reverse thrust while airborne is not possible in modern large aircraft. Reverse thrust is restricted to on-ground operation. Only after weight-on-wheels is determined, reverse thrust can be applied. $\endgroup$ – user7241 May 25 '15 at 19:31
18
$\begingroup$

Commercial jets are not designed to use reverse thrust in flight. With engines mounted under the wing, the turbulence can affect the lift over that section of wing. Tail mounted engines could interfere with the tail. This, in addition to the huge increase in drag, is what causes loss of control, as in the incidents that RedGrittyBrick mentions. Speed brakes are designed to provide the needed drag for emergency descents or otherwise slowing down faster. If the pilots find themselves too high/fast for an approach, and deploying spoilers/gear/flaps won't fix it, then they should go around for another approach.

The loss of control is more of a risk when a thrust reverser deploys only on one engine. Other risks are still there, since those thrust reversers are designed to deploy in landing conditions, not flight conditions. Notable exceptions listed on Wikipedia include the Hawker Siddeley Trident, though it also mentions that the capability was not often used.

Military aircraft, such as the C-17, can be different. They tend to make extremely steep descents more often (called a tactical descent/approach), so thrust reversers can be used in flight.

I did some testing with the stock 747-400 in X-Plane. Deploying the thrust reverser only changes the force applied by the engine, but doesn't seem to affect the air flow. So the loss of lift is not reflected by the model.

|improve this answer
$\endgroup$
  • $\begingroup$ It was years ago, but I was on a DC-8 that had been re-engined with turbofans. On this flight, they used reverse thrust in flight to lose altitude quickly. The Captain came on the intercom first to warn the pax of an unusual noise and vibration before he did it, and then he used the reverse thrust. Yes, it was noticible and a bit noisey in the cabin. I am glad he gave the pax warning. Concerning the pax may be a reason why this is generally not done, even if the plane is capable of this maneuver. $\endgroup$ – Skip Miller Nov 10 '14 at 21:40
  • 1
    $\begingroup$ years ago I saw a 747-200C use TR in flight during final approach to rapidly descend when it crossed the runway treshold way too high. Yes, it happens but it's rare. I think I've also seen incident reports of accidental TR activation in flight but that memory is very vague. $\endgroup$ – jwenting Nov 11 '14 at 7:26
12
$\begingroup$

It may depend on the aircraft and situation but an unintended deployment on one engine lead to the in-flight break up of a 767

At approximately 15 minutes into the flight and at approximately 25,000 feet altitude, one flight crew member commented that the reverser had deployed. This comment was immediately followed by evidence of a rapid airplane attitude change and subsequent in-flight break up, leading to airplane wreckage falling into remote jungle terrain approximately 94 nautical miles from Bangkok.

|improve this answer
$\endgroup$
  • 1
    $\begingroup$ Thanks for the link, I actually just finished reading about that same flight on Wikipedia. $\endgroup$ – jay_t55 Nov 10 '14 at 17:51
5
$\begingroup$

The Pilatus PC-6 (a turboprop) can be put the prop into reverse pitch and descend nearly vertically. Here's a demo https://www.youtube.com/watch?v=PU3RecxHRtk

|improve this answer
$\endgroup$
  • 1
    $\begingroup$ Note that the question is tagged boeing and boeing-747, so this answer doesn't really apply. $\endgroup$ – Lnafziger Nov 10 '14 at 21:28
  • 1
    $\begingroup$ No it doesn't apply at all, but if the goal is to teach people about the topic of reverse thrust while airbone, I think this does a fairly good job. $\endgroup$ – rbp Dec 3 '14 at 15:18
  • 1
    $\begingroup$ Well, as you know, the goal on this site is to answer the specific question that was asked instead of trying to answer variations of it. :-) $\endgroup$ – Lnafziger Dec 3 '14 at 19:05
3
$\begingroup$

As Skip Miller Mentioned the DC-8 thrust reverse was designed for in-flight operation.

Skip Miller:

It was years ago, but I was on a DC-8 that had been re-engined with turbofans. On this flight, they used reverse thrust in flight to lose altitude quickly. The Captain came on the intercom first to warn the pax of an unusual noise and vibration before he did it, and then he used the reverse thrust. Yes, it was noticible and a bit noisey in the cabin. I am glad he gave the pax warning. Concerning the pax may be a reason why this is generally not done, even if the plane is capable of this maneuver.

DC-8 Manual ,American International Airways, page 29

Descent rates of less than 4000 ft/min are sufficient for all normal Operations. A descent rate of 1 000 ft/min is about maximum that Will allow a precise comfortable Level off. This should be closely monitored when within 2 000 Feet of the ground. Reverse thrust, if necessary, may be used in normal descent at speeds above 1 90K IAS. When this is done it is limited to inboard engines only.

Lauda Air Flight 004 (NG0049) overview:

Some thrust reversers were designed for limited use in flight (such as inboard engines on the McDonnell Douglas DC-8)

|improve this answer
$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.