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I was aboard a DC9 a few years ago, I forget just where---Detroit, I believe. The airliner was backed away from the gate using reverse thrust. I have seen AirTran DC9's doing same in Atlanta. My questions: do engines equipped with cascade-type reversers provide as much reverse thrust as the clam shell, or bucket-type reverser? Could a cascade-typer reverser provide enough thrust to back an airliner out of its gate?
Don't know but its certainly not something I'd like to try! Apart from the noise, the hazard to ground crews and potential engine damage due to ingested objects, if you braked too hard you might tip the thing on its a rse!
Net reverse thrust in the 747-400 GE installation is, I've been told, about 40%.
The fan produces about 75% of total forward thrust, leaving 25% from the hot section. Theoretical max reverse, then, is 75% - 25% (hot section is still blowing aft), or 50%. Then there are efficiency losses in the cascade setup. Further, N1 speed is limited in reverse to about 95%.
It's a moot point, though, because reverse thrust for backing on the ground is prohibited by our Flight Handbook.
A few years back a BA Captain did actually back up a 767 using reverse before the FO could stop him. Happened somewhere in Turkey I think and resulted in an interview without coffee with senior management.
Used to reverse off stand in JER in the SD360. Used to make a lot of noise and if we were near max TOW the ground man used to have to push on the nose (seriously) to get us moving. He also used to get very wet if it was raining. P1 had to keep the steering tiller within 5º of centre (I think) or the castoring nosewheel would swing viciously against its stop and halt the entire proceedings. It was of course an approved procedure.
In my present company it is expressly forbidden on the 767 and allowed on the 757 only with specific Flight Management approval and then complying with the two pages of instructions in the flying manual. The whole procedure appears 'interesting' to say the least!
Wasn't the use of reverse thrust in poor weather blamed for ice/snow ingestion causing the loss of the aircraft which hit the Potomac bridge, a few years back?
During pushback on snow/ice covered ramps it becomes practical necessity to start up and to apply some reverse when the tug is spinning its wheels and going nowhere.
It's a normal procedure in the US for aircraft with aft mounted engines on the fuselage, DC 9, &!&,F100 etc. Just a tad noisy but no different than reversing a J41 or ATP as seen at MAN or such like.
Once again, thank you for taking the time to reply. I read about the Air Florida crash in one of Mcarthur Job's books. Reverse thrust did cause the engines to ingest snow/ice. Also, the NTSB decided that, after listening to the CVR, the engine de-ice (I'm assuming there is some type of pitot tube mounted inside the cowling?) item was answered "off", when performing the checklist. From what I could make of the report, this caused the pilots to use too low an EPR setting. At take off, the engines weren't developing all the thrust they could have, but, apparently, the pilots didn't know this.
The CVR transcript in Job's book clearly shows that the FO was not happy with engine instrument and speed readouts during the take-off roll.
Can't speak for others, but at my airline, when the ramp is "contaminated" by rain or snow, we stop powerbacks and go to all pushbacks. In the early days of the 747, we would often need help from the reversers to get our LHR-LAX flight of the gate
The "10" only has reversers on 2 of the Conways, so they must have had to work pretty hard (depending upon a/c weight, I guess).....sounds like someone forgot to pack the towbar!
No doubt if BEagle is reading, he will fill us in on the finer points!
Wycombe. The "full" story... Icy ramp, [the old B2] brakes on...still forward motion Then, as you say VERY loud noise. VC10 stops, then goes backwards until power/reverse is reduced when he stops we aim to please, it keeps the cleaners happy ps, it "may" have been a VC15, I think that they had four thrusters
"Wasn't the use of reverse thrust in poor weather blamed for ice/snow ingestion causing the loss of the aircraft which hit the Potomac bridge, a few years back?"
PT2 had frozen due to poor wx giving indications of higher than normal EPR. This tends to be the reason that crews x-check EPR with N1 during the T/O roll.
Saw this trick performed by Sterling Caravelle VI-R (Avon engines) at Manch c1975. Did a good job of sandblasting the spotters who remained standing on the pier roof (where they were still allowed in those happy days)
This was the way when I was young (or perhaps before that). Sure it looks cool but the risk is debris gets blown into the control surface mechanisms. Much better to get a pushback.
Oh PULease - all the naysayers that said it would screw up the engines or the airframes were proved wrong, over and over again. If you can powerback, powerback!
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