AA_Cam From , joined Dec 1969, posts, RR:
Reply 1, posted (13 years 3 months 3 weeks 3 days 5 hours ago) and read 6413 times:
The airplane uses its thrust reversers to "power-back" the aircraft. Since the aircraft is doing so under its own power, the engines are started at the gate, the aircraft moves slowly ahead a couple feet (to move off the flat spots on the tires) and then deploys its thrust reversers. It's an experence to see and feel. After the aircraft is away from the gate, forwart thrust is applied to slow, and stop the aircraft. This is important. Using the brakes to stop, during reverse motion, would shift the C of G aft the main landing gear, causing the aircraft to pivot around the main landing gear (acting as a fulcrum), and strike its tail against the ground.
After that, the aircraft can taxi out for departure.
This procedure is used as least often as possible, however, it is sometimes required due to lack of a tug. It may also be used if the aircraft cannot sit out on the ramp for the time it’ll take to start the engines (such as in a high ground traffic density area).
Bio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 3, posted (13 years 3 months 3 weeks 2 days 13 hours ago) and read 5754 times:
Something not mentioned is that powerbacks are only performed on high engine aircraft such as the DC-9, B727, MD-80/90s, B717s. Since the engine is higher, there is a low risk of debris ingestion by the engine. With wing mounted engines, there is a lot of ground debris blown toward the front when the reverser is activated, thus the risk of ingestion.
Goboeing From United States of America, joined Jun 2000, 2801 posts, RR: 14
Reply 7, posted (13 years 3 months 3 weeks 2 days 8 hours ago) and read 5717 times:
I know that the Air Florida 737-200 that crashed into the Potomac River on departure from DCA did a powerback before takeoff. I think this was being considered during the investigation. There's a risk of foreign object damage (FOD), like rocks, little stuff like that laying on the ramp, can get sucked in. I just looked, but could not find, a funny picture of a baggage cart that got sucked into a Delta L-1011 engine. If someone finds it, please post it!
Airplay From , joined Dec 1969, posts, RR:
Reply 9, posted (13 years 3 months 3 weeks 2 days 7 hours ago) and read 5713 times:
"Certification" for "power-backs" is generally a subject of operating procedures rather than aircraft certification.
Although some airplane flight manuals have a "limitation" that restricts power back operations, it's usually up to the individual airline SOPs and the particular airport rules. Many airports prohibit power-backs.
In my opinion, "power backs" should only be used in special circumstances. They introduce unnecessary risk to personnel at the gates and accelerate the wear and tear of the structures in and around the gate. All that extra soot isn't great either.
CLL777 From , joined Dec 1969, posts, RR:
Reply 11, posted (13 years 3 months 2 weeks 18 hours ago) and read 5512 times:
The only airplanes that use the powerback feature have the bucket type of reverses, I.E. the DC-9s and their variants, and the 737-200, all other aircraft use a different style of thrust reversers. Sorry if I missed an aircraft not a big fan of the smaller ones.
737doctor From United States of America, joined Mar 2001, 1332 posts, RR: 36
Reply 15, posted (13 years 3 months 2 weeks 12 hours ago) and read 5485 times:
Goboeing, you are correct about the Air Florida crash. After the tug failed to get enough traction to push the plane, the pilots tried unsuccessfully to power it back. While the snow continued to fall, the plane sat and waited while another tug capable of doing the job was found.
B747skipper From , joined Dec 1969, posts, RR:
Reply 17, posted (13 years 3 months 2 weeks 9 hours ago) and read 5455 times:
Essentially ANY airplane that has reversers could be "powered back"...
First it has to be "approved" and requires proper training...
Location of the engines.. for FOD has to be considered...
I was trained to do power back in 727s...
One time had to do a power back with another type, illegally... the only airport tug available had a dead engine... it was either that or put 180 passengers in hotels for the night, bitching about how bad our airline is...
Recently, I had to do a "partial" power back with a... 747-200... yes...
Same circumstances, full passenger load, the only tug capable of pushing us back had a failed engine... So they did locate a "small tug" (just heavy and powerful enough to push back a C-150)... they provided "steering" with the tow bar... and with our engines in reverse, we provided the "power"...
A tug has to do quite a job... in normal circumstances, for any airplanes, not only pushing a heavy aircraft, but also pushing "against" idle thrust, if the engines are started before push back...
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 6
Reply 18, posted (13 years 3 months 2 weeks 7 hours ago) and read 5444 times:
Notice the thrust reversers on DC-9's and successors have their axes of symmetry just off vertical? That's to prevent debris from being sucked back into the engine during reverse thrust.
The original DC-9 was apparently designed with a vertical centerline. One of my college classmates had a summer job at Air Canada in 1967 and he he;ped redesign the thrust reverser to the off-vertical configuration. Then Douglas incorporated their design into subsequent DC-9's.
This change was not meant specifically for power-back, though, it was primarily for normal landing.
Sebolino From France, joined May 2001, 3735 posts, RR: 4
Reply 19, posted (13 years 3 months 6 days 2 hours ago) and read 5314 times:
Please excuse my ignorance, I don't see how a thrust reverser behind an engine could make the plane go backward.
The force on the reverser is at most equal to the force on the engine, which would just make a total force of 0.
Or is there something else, like a vacuum behind the reverser ?
Can somebody give me the physical explaination (I guess it's fluid dynamics related, which I don't know much).
AmericanAirFan From United States of America, joined Jun 2004, 410 posts, RR: 2
Reply 20, posted (11 years 4 months 2 weeks 1 day 17 hours ago) and read 4673 times:
Ok I dug this forum up from the archives looking ofr this subject and to answer your long lost question the bucket type are certified to to do it because their reverse thrusters are high powered and push the thrust forward.
"American 1881 Cleared For Takeoff One Seven Left"
Aogdesk From United States of America, joined Jun 2004, 935 posts, RR: 3
Reply 21, posted (11 years 4 months 2 weeks 1 day 17 hours ago) and read 4670 times:
The engine runs at various thrust settings depending on the stage of flight, from FORWARD IDLE at engine start to FORWARD MAX THRUST (which may exceed actual takeoff thrust). In the same respect, once a reverser is deployed, the engine itself will still operate throughout its various power settings. There is no single "reverse" power setting. As the crew lands, the ground spoilers deploy (automatically, if armed), brakes are applied (automatically in some cases), but the reverse thrust is always controlled and adjusted by the pilot performing the landing. So it is entirely possible that an engine is at 80% or more thrust, but only in the other direction hence providing some impressive stopping distances. All of that air/thrust is simply displaced in the opposite direction. Hope this helps...
Starlionblue From Greenland, joined Feb 2004, 17427 posts, RR: 66
Reply 23, posted (11 years 4 months 2 weeks 1 day 16 hours ago) and read 4654 times:
I talked to a CRJ crew the other day and asked about powerbacks.
"It's been done in the simulator... But it's not an accepted procedure".
Also, they used to taxi on one engine so as not to hit the brakes all the time. Maintenance said no. Then they used to taxi on two, but with one of the engines on idle reverse. Maintenance said no again.
"There are no stupid questions, but there are a lot of inquisitive idiots."
FinnWings From Finland, joined Oct 2003, 640 posts, RR: 2
Reply 24, posted (11 years 4 months 2 weeks 1 day 14 hours ago) and read 4646 times:
I haven't ever seen jet aircraft powerback here at Helsinki or any other airport where I have been... However, Finnair ATRs does powerbacks all the time and I have seen some Saab 2000s of Blue 1 doing those as well.
: We used to use a power back procedure in the B737-200C/F at Canadi>n. These aircraft were equipped with a gravel kit. As the nose gear differs in the
: Ive seen several power backs and experienced them as a passenger. It was cool moving slight forward then rolling backwards. -AmericanAirFan
: Sebolino, one of the best metaphors for a jet engine (or any reaction engine including a rocket) is a balloon full of air (like a children's balloon).
: Not to sound too neive, but... Concerning Eastern's supposed power backing of 757s - don't the thrust reversers on those engines only reverse the bypa
: FL1TPA, I'm no expert on reversers but the fan typically generates in excess of 80% of the thrust for a modern turbofan. So without considering other
: A tug has to do quite a job... in normal circumstances, for any airplanes, not only pushing a heavy aircraft, but also pushing "against" idle thrust,