Reverse thrusts

[G-BBAE]

Howcome when i landed on BA767 G-BNWH it didnt use reverse thrusts, i didnt use them neither at JFK or MAN.

[Re-Heat]

BA do not generally use any more than reverse idle since brake wear is lower where the brakes operate at higher temperatures on modern carbon-fibre brakes, lowering costs of fuel use and brake replacement. This is not the case for older metal brakes however.

Reverse is however used where any limiting condition exists such as wet or contaminated surfaces of the runway.

Short turnarounds would also influence a decision as hot brakes on repeated short sectors can result in overheating of brakes, therefore greater use of reverse.

You will have had reverse idle in use.

[davethelimey]

Interesting answer - thanks.

[G-BBAE]

Thanks, completed but interesting.
On landing they only used speed break and flaps, but they did decrease throttle.
Would they have done reverse thrust in the air before landing?

[davethelimey]

No. Using reverse thrust mid-air is, as I understand it, pretty much guaranteed to crash the plane.

[Kestrel_909]

Was the DC9 or other not certified to use revserse thrust in air as means as slowing down?

[speedbird_heavy]

No. Using reverse thrust mid-air is, as I understand it, pretty much guaranteed to crash the plane.

Not according to the Concorde drivers and C17 drivers. The C17 can decend at 15,000ft per minute using reverse thrust.

[TopBunk]

G-BBAE

I suspect that you don't actually know what happened. I'm not trying to be confrontational, but tell what makes you think that reverse thrust wasn't used? What do you think indicates the use of reverse thrust - what are you looking for/at?

Whilst the use of FULL reverse thrust will make a noise and cause a little vibration/shaking felt through the airframe, idle reverse will not be noticeable without looking outside.

As was said, idle reverse is the norm at BA, and monitoring programs will pick up when not used and questions potentially asked of the crew.

[BN2A]

And if you were sat by a window looking at the engine and no cowling movement was observed, the reverser was probably locked out on that engine for any number of reasons.....
The other would have been in reverse idle so as not to have a large assymetric braking effect.

:cool:

[davethelimey]

I'm not sure the 767 is directly comparable to either Concorde or the C17. Unlocking the reversers on a 767 (though I stand to be corrected) would bring the plane down very fast, if not uncontrollably, and BA wouldn't use reverse thrust during flight.

[G-BBAE]

So would a plane be able to land just using spoilers and flaps, but decreasing throttle, not using reversers.
Maybe the 767-300 reverse thrust was quite.

[davethelimey]

It's unlikely that no reverse thrust was used, but it's more than likely that idle reverse thrust was used - the reversers unlocked (ready for the unexpected) but the engines not powered up. it would've been quiet.

[G-BBAE]

Which aircraft tend to have the loudest reversers, flying on an MD83 ive noticed they can be very loud.

[TopBunk]

GBBAE

Reversers aren't loud in themselves, reversers merely deflect the jet eflux in a different direction. On modern jet engines they usually just reverse the cold air (that has bypassed the combustion process) leaving the hot stream pushing you forward. Older engines such as the P&W JT8D's on 737's etc had clam shell reversers that reversed all of the flow and were much more effective - I think MD8x's use this technique.

As to noise, if an aircraft uses idle reverse thrust the noise will ne minimal, only when the engines are accelerated above idle reverse does the noise increase. Older engine types are noisier than newer types. It is very noticeable when an aircraft uses full reverse at LHR as the vast majority only use idle - just wait until Air India lands to see what I mean!

[davethelimey]

To say nothing of the fact that on an MD8x the engine (depending on your seat) can be right outside the window.

[mutt]

GBBAE,

Thrust reversers arent very effective on dry runways, the aircraft was certified for landing without using them. Most airports have noise restrictions on the use of more than idle reverse thrust. So dont be surprised if you see aircraft using idle reverse.

As for reverse in the air, Lauda Air lost a B767 in Bangkok following the opening of a thrust reverser after takeoff.

The Trident and CV880/990 were some of a limited number of aircraft capable of using reverse inflight. Maybe also the DC8.


Mutt.

[Dr Illitout]

BN2A Both NWH's thrust reversers are sevicable and have been for quite a while.

Rgds Dr I

[Flap 5]

1. Modern civil jet airliners can not deploy their reversers in the air as they are activated by the undercarriage squat switch, unless the system has failed. On some aircraft types you can pull up the reversers prior to landing so that the squat switch will deploy the reversers immediately after touchdown. This is not encouraged in case of a failure of the safety system preventing deployment in the air (i.e. the squat switch).

2. Civil aircraft are certificated for landing distance without considering the effect of reversers.

3. Reversers are used generally at heavier landing wights, are only really effective at high speed and are reduced to idle below 80kts. Using reversers above idle at slow speed risks ingesting stones, etc. into the engine.

[look you]

Flap5,

Not all aircraft have reversers tied into squat switches, by any means. The 737 has a Rad alt ht of 10' as the earliest reverser opportunity. This is to ensure that they are IMMEDIATELY available after landing, especially on slippery runways where they may be the only retarding force.

Without this, If you lose a squat switch and land on a slippery runway which prevents your wheels from spinning up you are in trouble!!

Mutt,

Why are reversers less effective on a dry runway???

Surely you mean they may not be used because the brakes are MORE effective? You cannot change the laws of physics, the same backwards force out of the engine will produce the same retardation, wet or dry?

Try applying your argument to forward thrust, are the engines less effective in the wet? Is that why V1 wet is lower than V1 dry??


I fail to see why using reverse idle in the air would have an instantly catastrophic affect on many aircraft. As long as it is SYMMETRIC!!!!

:D

[mutt]

look you.

Looking at a required stopping distance chart showing the various combinations of brakes/spoilers/reversers on a dry runway, its easy to state that the reversers arent very effective, but as you stated its because the brakes are MORE effective.

Mutt.

[Ray Darr]

Mutt: re DC-8's... yessir, inboards are used to drop out of the skies for emerg. descent (but NOT used for ducking back to the glide when turned onto finals too early!!). :p

BN2A: You are bang on about using idle reverse only when one is locked out... of course many of us have been guilty of briefing "Idle reverse only on the good one" then after a long duty-day / long block of min rests...we still slam them into full reverse with a "AHHH CR@P!" then correct ourselves by zipping it back to idle with nothing harmed but our foreheads from smacking one's self for the boo-boo... :O

Cheers,
Ray Darr

[john_tullamarine]

... although probably a tad politically incorrect ... it's a wonderful sensation when one rips in a fistful of reverse after touchdown ... almost as good as .. no ... we aren't allowed to use old technology engines any more, are we ... ?

[CrashDive]

.... and especially so when the runway lights whites have turned to red & white, and even more so when they've all become red, and / or the runways wet / slippery and all you're thinking is..... "Ohhhhh sh#t, come on, stop you bugger !!!" ;)

[dusk2dawn]

Cubana IL 62 , reversers deployed before touch-down ? (http://www.airliners.net/open.file/017016/L/)

[sp]

[Flap 5]

The IL 62 is an older generation aircraft. Look you is correct about the 737 allowing the reversers to deploy at 10 feet radalt. However that part of the 737 design has been carried forward to the later 737's, including the NG. Therefore the 737 reverser design is essentially older generation as well from the 100 and 200 series. I think if you look again at my post I did say modern civil jet airliners.

The Trident could also deploy reversers just before touchdown (10 feet is at or pretty damn close to touchdown) and frequently did so for short runways such as Aberdeen and Milan Linate. The latest design of commercial jet aircraft use the air/ground safety sensor (or squat switch) to allow deployment of the reversers.

[Touch'n'oops]

Remember that the thrust reversers are most effective at high speeds. Same goes for the Spoilers.

At my airline we try and keep the use of brakes to a minimum. This is because our turnaround times are so short. If brakes are used excessively on landing our Vmbe maybe exceeded for take off. Thus when the day comes to hit the brakes, they overheat and 'brake fade' becomes more than a couple of lines in the training manual!!!:oh: :oh: :ooh:

[Md-driver]

Mutt: Required landing charts for dry runways do not include reverse thrust. This is a certification rule. Reverse thrust is only included in contaminated runways. In the Lauda case i think that the problem was not the reverser deploying but the fact that the engine was running at high N1 when the reverser deployed. When manually activating reverse you first go to idle thrust which I don´t beleive would cause a problem in flight. However as the reverser in the Lauda flight extended by itself it did so at a high thrust setting causing interupted airflow over a section of the wing as well as developing a significant yaw.

[mutt]

Md-driver

Required landing charts for dry runways do not include reverse thrust That is very true, however those nice people in Seattle publish a B747 graph with required stopping distances based on different configurations!

Point taken about the Lauda, thanks.

Mutt.

[stilton]

Didn't Lufthansa have an A320 that overran with fatalities due to
the inability of the pilot flying to activate reverse or deploy spoilers due to air/ground sensing thinking the aircraft was still airborne.

[PT6ER]

Flap5

The later versions of the 737 have the CFM56 engine and therefore have a cascade style of reverser. The JT8 versions had the bucket/target style. Whether or not the reversers can be used in flight is down to two things:

1. Was the airframe / reverser combination certified using controllability (sp?) - if so, then the structure supporting the TR is stressed to take flight loads with full power deployment and flight testing has proven the controllability of the deployed TR / airframe combination

or 2. was the system cerified using system redundancy to ensure no inadvertant deployment. If this method is used, the structure is not generally designed to take inadvertant in-flight deployment loadings. The likelyhood of in flight deployment has been mitigated to such a small number by the use of a multitude of interlocks that to carry sufficient structure around is not efficient nor required.

As an aside:

Does anyone know of other military fast jets (apart from the Tornado) that have thrust reversers??

[Dan Winterland]

The 767 you were sat in will have used idle reverse and autobbrakes. Modern carbon brakes work better when hot and wear out quicker when the application is applied more than once and/or varied. BF Goodrich (the manufacturer od the majority of carbon brake systems) state that the reccomended technique is to use autobrake and idle reverse. Autobrake sets a decelleration rate measured by the inertial reference system rather than a brake pressure (unless you use setting MAX or RTO where you get the full system pressure).

For example, setting 3 on a 747-400 gives you a rate of 4 feet per second per second and if you bring the reversers up above idle after touchdown, by the time you have spooled the engine up in reverse the brakes would have already been pressurised and the system will reduce the pressure to maintain the decceleration rate. When you stow the reversers, the brakes will modulate again, so you have three changes in braking rather than one thus wearing out the brakes more, making more noise and putting more stress on the engines.


I think the SAAB Viggen has reverse thrust as well.

[Flap 5]

PT6ER,

Engine type is irrelevant. It is how the reversers are activated that matters. Both the JT8D powered 200 series and the CFM56 powered 300 and NG series have reversers activated by 10 foot radalt or the air/ground safety sensor. Your point is spurious and irrelevant.

[PT6ER]

Flap5

Sorry for deigning to disagree with you but, and I quote,

"Therefore the 737 reverser design is essentially older generation as well from the 100 and 200 series. I think if you look again at my post I did say modern civil jet airliners."

The design of the reverser is most definately not "older" by which you meant (I thought) a target type.

I was not commenting on the design of the control architecture (SP?) although the safety interlocks required on modern reversers far exceed anything used in the past (I think the Lauda Air incident drove a lot of the changes). It is interesting to note that some modern target type reversers (and I have worked on the design and certification of three so far) are aerodynamically unable to deploy above a pre-determined power setting. Some bizjets are certified using controllability and some using system redundancy - horses for courses really

My comments are not spurious nor irrelevant and were left as an addition to a good thread, not as any personal jibe. Calm down and re-read my post.

Remember the "Word" according to Bruce Hornsby.....

"That's just the way it is"

:ok:

[Flap 5]

I see. You're trying to blind me with science. :D

[PT6ER]

It is probably breaking all the rules to admit this but I am an engineer......

Dont think any less of me!!:p

[Flap 5]

Ah! I sensed that. :D There was that natural antagonism that exists between a pilot and an engineer! I usually get airborne in an aircraft just after an engineer has 'fixed' a problem only to find it reoccur. I get this irrational urge to shake the engineer warmly by the throat! :suspect: :D

By the way I tried to post yesterday but the site had crashed. Obviously an engineer had been let loose on it! :rolleyes:

[elemenohpee]

Reverser's Deployed!!

First Officer Josef Thurner, Air Lauda 004
Last recorded words during "impossible" in-flight ddeployment
of the B-767's Reverser
26th may 1991

obviously not a good thing!:(

[PA-28-180]

Don't know about large civil aircraft, however, I once saw a Lear 25 landing at Columbia airport in California with his reversers half deployed at approx 1/2 mile final and 400 AGL. Have a feeling this was NOT something found in the aircraft's POH.:uhoh:

[bombinha]

Hi PT6ER I worked in an Airline that the reverse (probably one of those you worked on the project) was designed to never open for aerodinamic reasons below 200kts once airborne in case of squatch switch failure so how come it did opened and killed 99 people 94 on the airplane and 5 on ground just after rotate at about 150kts or less?
So my point is and I think that is what the other guys try to say is, they fail because there is no perfect system as there is no perfect human.
I agree they don't fail very often but they do fail and as far as I know the Lauda Air case nothing was done just the fact of PW4000 lost theyr certification to use reverse in flight as speed brakes therefore deactivated this function.

[rubik101]

B737 repuires BOTH gates to be open: 10 ft RadAlt AND the squat/weight switches to be made. Reverser deployment in the air is unavailable, prohibited if it were, and undesirable on any account.

[PT6ER]

bombinha

I have never worked for Boeing but I do know from friends that they went into design overload after the Lauda Air incident to redesign the reverser systems.

I'm surprised the PW4000 reverser was certified for in-flight deployment in the first place - may be an ex Boeing person could clue us in on this.

I agree on the "no perfect system" since the only truely safe aircraft is the one that never flies (even then you could trip over the landing gear I suppose :D )

The science is to produce a system that has a probability of inadvertant deployment so low as to be acceptable to our good friends at the FAA.

Going back to certification by controllability, the TR has proven by testing and/or analysis that it is structurally adequate during deployment at certain prescribed airspeeds and power settings, maybe the Lauda Air TR was certified using system redundancy - that is pure speculation on my part.

I've been away from reversers for a while but the probability numbers (for inadvertant deployment) generated by the system Failure Modes and Effect Analysis (FMEA) need to be extremely small.

I guess what I am rambling on about is that we endeavor to reduce/mitigate the risk to an acceptable level....by definition it cannot be eliminated.

Apologies for any spelling errors - I'm asn engineer, we are not supposed to be able to spell ;)

[Final 3 Greens]

The Trident could also deploy reversers just before touchdown The Trident could use reversers from any altitude, see Arthur Whitlocks book "Behind the Cockpit Door", for a memorable war story about an emergency descent into PMI after a pax cut her fingertip off in the loo door.

They got down safely and the finger was repaired successfully.

When I tried the same in the sim, the RoD was about 15Kfpm.

[Flap 5]

rubik,

My Boeing 737 Operations Manual in the section for Engines, APU (page 7.20.8 paragraph 3) states quite clearly: 'The thrust reverser can be deployed when either radio altimeter senses less than 10 feet altitude, or when the air/ground safety sensor is in the ground mode. Movement of the reverse thrust levers is mechanically restricted until the forward thrust levers are in the idle position'. There's no and in there (or even AND).

Undesirable it may be, but possible.

[PT6ER]

Flap5

Just to show my ignorance, does the rad alt measure from the bottom of the fuselage? So would less than 10 feet mean that the gear is in contact with the ground or just above it?

Is the "air/ground sensor" a posh phrase for a squat switch?

My knowledge turns to "general" at best, beyond the firewall ;)

Thanks in advance for the answers.

[Flap 5]

The transmitter and receiver for the radalt is on the underside of the fuselage. So at 10 feet radalt the wheels are just above the runway. The main danger of this in practical terms is if you had cracked the reversers open in the flare, by raising the reverse levers a bit too soon, and then initiated a go around. This could happen on a low visibility approach if you found yourself close to the edge of the runway or with a runway incursion as you are about to touch down. The reversers should stow but if the system stays in the ground mode they will not and then you have a dangerous situation.

Yes air/ground safety sensor is american for squat switch (why use two words when four will do!). :D