Few questions about reversers

[pkonowrocki]

hello.
I was searching the db and found this picture of Aeroflot Tupolev TU-154:

[photoid=5838234]

The picture shows the airplane using reversers when still in the air - before touchdown. the comment says that it is a "common practise for TU-154".

So I have a few questions about them - reversers. First of all I wanted to know how they actually work - how they bring airplane to stop and do the pilots always use them ? Also Are you allowed to use them anytime or are there any certain limitations ? can you use just one reverser or do you have to use all of them? And is there any other aircraft where pilots user reverser when flaring or is it just TU-154. And why they do that?

Hope somebody can help me

[JordanD]

Well, I can't answer all those questions, but I know that you're supposed to use all reversers at the same time. The reason being if you don't, you'll have asymmetric thrust. Basically, the plane will yaw towards the engine that's developing less power. Planes like the DC-10, 727, TU-154 would be an exception as they could use only the center reverser I guess, but I wouldn't see the point. Hope that answers some of your question.

[N9103M]

Generally reverser use is restricted to ground use only. Any airplane equipped with reverse (including reverse pitch on turboprops) can use it to back up on the ground. However, most airplanes with wing mounted engines are restricted from powerback operations due to the high likelyhood of ingesting ramp debris when reversing. (Aulthough I have seen 737-200's powerback)

To counter this, most airplanes with reversers have limitations to have the reversers stowed or at a idle power setting by around 80 knots. MD-80's have another limitation of 1.2 EPR in reverse because it disrupts the airflow around the rudder, reducing it's effectiveness early in the landing roll, before nosewheel steering can be used effectively and safely.

Thier use in flight is VERY rare, and in most cases prohibited. If one were to deploy in flight, it could cause a disaster. (See the Lauda B-767 crash in the 80's in Thailand) The only non-Russian airplane I know of that is certified for in-flight use of reversers is the DC-8. You can reverse the two inboard engines in flight. I have ridden on the jumpseat once when the crew did that to get down (The DC-8 has no flight spoilers) and the airplane shook quite violently. But the -8 is built like a brick sh*thouse so it can take it. Most operators still prohibit it due to the stress on an already old airframe.

On landing, you always want to use symmetrical reverse. Asymetrical reverse on an airplane with wing mounted engines can cause serious ground control problems. I once had a propeller govenor fail on me as I selevted reverse in a Shorts 360 and the left engine stayed in idle and the right engine went into full reverse, it took all of my might on the tiller and power to correct back to the centerline and stop from going off the side of the runway.

Asymmetrical reverse on an airplane with tail mounted engines is barely noticeable. On the 727, with any engine out, you can select reverse on the other two engines and feel very little pull. Same went for the CRJ.

On the 727 specifically we use #2 reverse to help keep taxi speed low and keep the brakes cool, especially on long taxis. This is approved and not approved on some airplanes.

As far as the Russians and the deploying reversers before touchdown, you have got me, there is no western equivilant to that as far as I know.

[Colin Parker]

Actually, whether you use symmetrical thrust or not really depends on the aircraft type. On the 777, the engines are mounted close enough to the fuselage that if one reverser is inop, we still use the other one. There is hardly any pull to one side when you use even full reverse, let alone control difficulties. It just depends on the aircraft. On the 747 when we had a reverser inop, we always used to only use idle reverse on the opposite engine.

[AJ]

Well, I can't answer all those questions, but I know that you're supposed to use all reversers at the same time. The reason being if you don't, you'll have asymmetric thrust. Basically, the plane will yaw towards the engine that's developing less power.

Quite the opposite in reverse thrust......the aircraft will yaw towards the engine developing more power!

[N9103M]

Actually, whether you use symmetrical thrust or not really depends on the aircraft type. On the 777, the engines are mounted close enough to the fuselage that if one reverser is inop, we still use the other one. There is hardly any pull to one side when you use even full reverse, let alone control difficulties. It just depends on the aircraft. On the 747 when we had a reverser inop, we always used to only use idle reverse on the opposite engine.

You know, since I've never flown a jet with wing mounted engines, I probably should have shut up on that point.

Thanks for the help!

[pkonowrocki]

Wow thank you for such detailed info. Now I know everything about reversers. Btw. how do you guys know taht ? Are you all working as pilots ?

[JordanD]

Some of us are (not me obviously :P) I think the Pilot's handbook of Aeronautical knowledge has some stuff on it. It sure makes a good sleep aid though.

[N9103M]

Wow thank you for such detailed info. Now I know everything about reversers. Btw. how do you guys know taht ? Are you all working as pilots ?

I'm a 727 F/O for a cargo company in the US. Previously I've been a Captain on the Shorts 330/360 and Falcon 20, and an F/O on the Beech 1900D and CRJ-200.

[pkonowrocki]

I'm a 727 F/O for a cargo company in the US. Previously I've been a Captain on the Shorts 330/360 and Falcon 20, and an F/O on the Beech 1900D and CRJ-200.

Wow that's sick. Are you working for DHL or FedEx flying their 727s ?

[Colin Parker]

I am a SFO on the 777-200 and -300....and what fun it is too!

[LRJet Guy]

We're prohibited from going below flight idle until the nosewheel is on the ground in the Dash 8 for the reason 9103M stated. If one of the props doesn't respond, you're off in the weeds. We rarely use reverse in it.

In flight, disc and reverse is locked out on the aircraft. You will get a horrible chirping alarm if you lift the trigger, and the engines will actually do the opposite of what you ask if you try to select reverse. It will also lock out the computers on the engines, which is the tattle tale feature that will land you in hot water with the Chief Pilot, and possibly the FAA.

The only jet I flew with reversers was the Sabreliner, and we did not use assymetric reverse thrust. With the narrow track of the main gear, it's enough of a handfull on the rollout. Reversers are also locked out on that aircraft in flight. Emergency stow is selected for takeoff, and landing until just before the mains touch.

[MCM]

As 3M points out, backing up on the ground with the reversers is in most cases frowned upon. 744 Limitations manual expressly forbids it.

Inflight, its definately not something you'd want to see!
A "reverser unlocked" indication inflight usually attracts some attention, and if it actually deployed, well, we know what can happen.

With the moment created from the outboard engines on the 744, you really wouldn't want assymetric thrust... most companies say symetric thrust only, and idle reverse on the other operative engine in the engine inop case.
It wouldn't take long to be visiting the edge lighting, and the grass on the side of the runway, unless you really were ready for it.

Interestingly, assymetric thrust does have its uses... if you find yourself on a really slippery taxiway/runway and have limited steering control, reverse thrust can be used to keep you straight. But its best not to get into the scenario of needing that one!