Reversers on in midair

[Guest ChrisTrott]

Andy, you can probably confirm this too-The Concorde procedure is not actually a full deployment of the inboard reversers either, rather a partial deployment to divert some flow. That was the understanding I got from a British Airways pilot I chatted with one night (British time) on a chat room.Also with the midair- the DC-9/MD-80 reversers are held closed by hydraulic pressure and if 2 lines are severed, it will cause the reversers to deploy from the airstream passing across them with the loss of line pressure to hold them closed. This has also occured on other aircraft with similar systems.The other possibility is that he bypassed the squat switch by using the emergency reverser override system. This is not supposed to be used in flight and was/is not approved under any circumstance by Douglas's manuals. You can do this on many current systems, but flight crews know what happens what might happen if they do.

[Guest B52Drivr]

ABsolutely excellent reply . . . to the point and correct!Clayton T. DopkeMajor, USAF (retired)"Drac"B52Drivr@aol.com

[Guest ChrisTrott]

Gotta kill the C-17 pilot who told me that then... Wish I had time to go out to Charleston. I'd read the Boeing thing as well and asked that of the C-17 crew when they visited Denver a few weeks ago, and the pilot told me that they can't do it for the reason I specified. Aparently they've had a couple of planes come back after doing that with cracks on the pylon mount pins and I've heard stuff through other military contacts that they did actually have a C-17 during OpEval loose an engine while performing inflight reversing.

[Guest AndrewW]

Hello Chris, The reverse buckets on Concorde are referred to as secondary nozzles, which when used in flight in reverse idle, move to 23 degrees. Full reverse places the buckets at 73 degrees. At low speeds (below M1.1) the nozzle angle scheduling unit (NASU) positions the secondary nozzle as a function of Mach number and also provides the appropriate signals for the automatic selection of control schedules. There are two NASU systems, No.1 system signals engine 1 and 4 and No.2 system signals engine 2 and 3. Protection against inadvertent bucket movement toward the reverse thrust position is done so in the following manner: Should the bucket move beyond the 27 degree position, an air shut off valve cuts the air supply to the bucket drive motor. This should prevent bucket movement beyond 35 degrees. If however the buckets move beyond 42 degrees a 'wind down' system operates and signals via the selected throttle control system a reduction of N2 to idle. Part of the pre-departure checklist is to check the NASU system (the air shut off valves), by advancing the throttles, placing them back to normal idle, and then into reverse idle - known as a 'reverse air shut off check'. It has been known for the buckets to run-away towards the reverse thrust position in flight, which is why these systems are so vital to the aircraft (hence the pre-departure reverse air shut off check). This situation is taken into great consideration on Barbados trips, where for a small sector of the flight, there is no alternate for a 2 engine failure. If such a situation with the secondary nozzles were to develop, and the NASU systems failed - the engines would have to be shut down. An aircraft that is scheduled to make a Barbados trip will fly a NY trip in the week to ensure that the systems are fully operational. Andy[/font size]

[Guest ChrisTrott]

Thanks for the confirmation of that. So, in essence this isn't a full "reversing" operation, simply a wierd form of speedbrakes. :)This system is also similar to a system developed for Light Jets (like the CJ-1 and CJ-2) where a simple deflector plate pops out from the rear of the engine pylon to divert the airflow. Not quite an airbrake and not quite a full thrust reverser... Kinda wierd to see them in action, but from what I understand, such a system (on both the Concorde and light jets) deployment of the panels produces as much induced drag from not being streamlined with the flow of air as it does braking action through the diversion of exhaust flow.

[Guest IanH]

>Alrighty now...>>TOO MUCH MISINFORMATION IN THIS TOPIC...>>Sorry for the CAPS, but it's needed.>>1) Thrust reversers are NOT deployable in the air on ANY>AIRCRAFT. >Thanks for reading this guys. Only thing I request is that>you guys do some research before providing answers and confirm>what you think you know. It only takes a few minutes and>saves on a lot of confusion.>>:)Sorry to step in here but this is not entirely correctThe Russian Ilysuhin Il62 is capable and has been seen to use the thrust reversers on the two outboard engines to aid in short field approaches.Page 13 of the current AIRLINER magazine shows a Il62 in the flare but still at a height of about 10 feet clearly showing the buckets deployed.RgdsIan H

[Guest ChrisTrott]

And according to another post in this same thread, this appears to not be an approved procedure, even though it's done, so I have to wonder if this is done in an override mode. I know that the TU-154B models can use idle reverse on theirs and it's approved (and even normal) but they're not bucket types, they're clamshell-cascade, however the stuff I've read on the IL's and the TU-154M say that they don't do that anymore (at least approved by the manual). The information I go off of is the approved procedures manual, which in some cases is ignored.BTW- I haven't corrected one thing because of the stupid edit timeout thing, but that should have read - ANY MODERN COMMERCIAL AIRCRAFT. Some of the older designs (like the IL-62 and DC-8) had the capability, but no currently produced aircraft has the ability. The C-17 is the only military one I know of that has the "capability", however I'm not sure (due to conflicting information) whether this is operationally allowed.

[Guest]

Well,dc-8 mechanic or not, I'd say since there were so many different models produced that operating procedures varied over time and model.Douglas definitely had some guidelines for using inner engine reverse as "descent brake", as long as You maintained more than 190kts IAS. Maybe that changed later.For unbelievers, search airdisaster.com or airsafety.net for the Alitalia DC-8 accident (at JFK or LaGuardia, not sure) where the captain selected idle reverse to slow the DC-8 down on final and ended up with some millions dollars's worth of aluminium trash. Fortunately, evacuation was successful.Torsten

[Guest BC_KBOS]

Now that we all agree that reverser use in flight was at one time marginally approved/acceptable, lets move on to the chase.What were they thinking?At the time, we had engines that would overtemp if you looked at them funny, reliability was, well, pretty good at best, and did anyone ever do an analysis of the effects on the pylons?Way back when, the A6 Intruder had speedbrakes that extended out from the fuselage directly in the path of the engine exhausts. When airplanes started dropping like rocks, the engineering types said "hmmmm, maybe we shouldn't put the speedbrakes there.."Seemed like a pretty good idea at the time. We learn from this stuff and I would hope that the lesson takes.Think ahead.BC

[Guest]

The main problem seems rather to be the possible rip-off of an engine, the pylons are quite stable in longitudinal direction, else the engines would come off while reversing on ground, too.The possible overheating *may* be a problem, but the worst parts still are:1) torque/yaw: the aircraft will violently start to yaw left or right, thereby risking stress problems to rudder etc. Less pronounced on 4-engine aircraft due to 2) partial wing stallthe exhaust plume of the reversers is more thank likely to disrupt the airflow over a portion of the wing, therefore creating a partial stall / dropping of wing, adding to roll and yaw momentumfor rear-mounted engines, the plume may affect airflow over the tail (rudder/elevator)Torsten

[Misha_K 0]

Not to utterly beat this topic to death, but I would like to question the issue of the nose squat switch in modern aircraft. From personal experience and the photo evidence below, I would think that the reversers are enabled by a main gear squat switch. I have seen numerous aircraft deploy thrust reverse well before the nose gear is down.See e.g.:A330:http://www.airliners.net/open.file/375467/M/http://www.airliners.net/open.file/372409/M/A320:http://www.airliners.net/open.file/371317/M/A340 (this one seems barely to have ground contact at all):http://www.airliners.net/open.file/297875/M/737:http://www.airliners.net/open.file/364971/M/747:http://www.airliners.net/open.file/328555/M/http://www.airliners.net/open.file/226863/M/http://www.airliners.net/open.file/189054/M/For the aforementioned aerial deployment of the outer reverser buckets on the Il-62 on short final see: http://www.airliners.net/open.file/348313/M/http://www.airliners.net/open.file/298669/M/Getting back to the squat switches, I don't have info on this, so I welcome someone else's thoughts, but I'm thinking these things were made a bit more sensitive after the Lufthansa A320 crash in the early 90's at EPWA. In this case the aircraft overran the runway, hit an embankment of sorts and caught fire, because the thrust reverser activation at the time required the main gear wheels to be rotating, which did not occur in time due to severe hydroplaning on a drenched runway. Anyone know more?BTW, I was spotting at EDDF a few weeks ago and some cowboy used thrust reverse to slow down a C-17 from a fast taxi to make the turn onto the rwy. Misha

[Guest]

< Only thing I request is that you guys do some research before providing answers and confirm what you think you know. It only takes a few minutes and saves on a lot of confusion. >Chris, I remember taking a flight from Rome to Jeddah in 1975 on a stretched DC-8 belonging to Alitalia. As we approached Jeddah we were still at something like 20000ft. Whilst I was wondering why we were so high (on Saudia 707's we were usually down to 5-6000ft at that point), The DC-8's nose went down steeply and the engine noise increased considerably. The effect was like being in a car when the brakes were applied. Looking out of the window I could see that the inboard engine where I was sitting (No2) had the thrust-reverser extended, and the steeper we descended the more the throttles were opened on the two inboard engines. It was a weird feeling and quite frightening to someone who is accustomed to traditional approaches. I don't know of any other aircraft that is approved for such operation, but Alitalia was a large operator of DC-8's, and can't believe they would operate the aircraft outside of the envelope approved by Douglas.I believe that a similar manoeuvre was attempted on an early 707, which subsequently crashed when the airflow prevented the reverser from being stored again. Can't find details on that though.Happy LandingsJohn

[Guest]

Can't speak about Twin Otters, but in all the same-engined (PW PT6A) King Air series I have flown (90, 100, 200 series) there is no electrical (i.e. squat switch) means to prevent inadvertent reverse activation. The whole design is mechanical, a substantial "gate" in the power levers travel at the idle stop position to get over. After pulling back to the idle stop, you have to actually lift the power levers up about an inch, before you are physically able to pull back any further into the beta and reverse ranges. It is thus physically impossible to reverse prop angle while making power above idle. --BeachComer Stephen "Beach" Comer Real World Pile-it Commercial ASMEL, Instrument Airplane 4500 TT, 2500 BE20 & BE10 Serving Happy Landings Since 1973!

[Guest]

Michael Crichton's Airframe is about an airliner which accidentally deploys its thrust reversers in mid-flight. It's a really good read, highly recommended.Regards-