N243NW From United States of America, joined Jul 2003, 1565 posts, RR: 21 Posted (9 years 9 months 2 days 23 hours ago) and read 3986 times:
I know the system is different between the aircraft models and manufacturers, so can any pilots or techies here explain how the thrust reversers are physically engaged and used in different aircraft (the procedure and steps involved)? I know that most/all of Boeing's planes have the reverser handles forward of the thrust levers, and if I'm not mistaken, Airbus's newer models have simple push buttons instead. Also, do any of today's commercial airliners have the capability of arming the reversers for landing? Can anyone elaborate on this topic?
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 1, posted (9 years 9 months 2 days 22 hours ago) and read 3886 times:
I believe that most of the airliners flying today can have their thrust reversers ARMED prior to landing, as well as their ground spoilers and auto-brakes.
Once the airliner's main landing gear has compressed enough apon landing, "squat switches" on the gear make contact and they send a signal to the airliner's computers that the aircraft is infact on the ground, and then the reversers, spoilers & brakes are automatically deployed & applied.
I think these squat switches need to have contact for a specific amount of time (a few seconds), to ensure the airliner isn't going to bounce back into the air before the computers will activate the auto controls.
I believe some airliner's computers also depend on main gear wheel rpm to ensure the airliner is on the ground before these auto systems will activate.
Also, you can ARM the TR's, spoilers, brakes, (and the cabin pressure dump valve I believe) all you want before touchdown, but the computers won't activate them if the airliner isn't in landing configuration with the throttles at idle (meaning the pilots are not doing a touch and go) and with the flaps/slats at a landing setting.
This is basic info off the top of my head that I've learned from this forum. It may have some errors although I think I've got it pretty much correct.
I hope the professionals in here will expand on this info with more detail for you.
OPNLguy From , joined Dec 1969, posts, RR: Reply 2, posted (9 years 9 months 2 days 22 hours ago) and read 3874 times:
I usually leave these kinds of questions to the pilot folks, but I have to note that the thrust reversers must be manipulated by the crew in order to actually deploy. Both the reversers and ground spoilers use the info from the squat switch that the aircraft is on the ground, but, if armed, only the ground spoilers "automatically" deploy.
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 3, posted (9 years 9 months 2 days 22 hours ago) and read 3860 times:
> OPNLguy, thanks for making sure my info about the TR's was corrected. It makes sense that the pilots would physically move the throttles for the TR's so that they are only used as long as they're needed.
I guess I was thinking about auto-throttles or perhaps my fingers were typing faster than my brain was thinking.
N243NW From United States of America, joined Jul 2003, 1565 posts, RR: 21 Reply 4, posted (9 years 9 months 2 days 22 hours ago) and read 3855 times:
So OPNLguy, you're saying that while there is a wheel spinup/squat switch for the reversers, the switch is simply a lockout to prevent inadvertent deployment in the air, and there is no actual automatic deployment unlike the spoilers and autobrakes? Also, keep in mind, pilots, that I'm also interested to know (procedure-wise) how the pilots manually engage the reversers even if they DO automatically deploy. Thanks for the replies so far!
Gearup From Canada, joined Dec 2000, 578 posts, RR: 1 Reply 5, posted (9 years 9 months 2 days 22 hours ago) and read 3856 times:
In the case of the Boeing 737-200 and 707 series, the reverser levers were forward of the throttles and could only be pulled back over the throttle levers if the throttle was at idle position which would or should be the case at touchdown (at least I think so!). This action by the pilot would operate the hydraulic actuators on the reverser, thus unlocking and deploying it. BTW, I really like the way the 737-200 reversers deploy! The reverser mechanism on the P&W JT8D engines is completely external and you can see everything going on if you are in a good window seat. In fact, the first time I saw it operate along with the spoilers extending and the flaps at full, I thought for a minute the wings were coming apart, there was that much stuff moving!
N243NW From United States of America, joined Jul 2003, 1565 posts, RR: 21 Reply 7, posted (9 years 9 months 2 days 21 hours ago) and read 3832 times:
>>>throttles or perhaps my fingers were typing faster than my brain was thinking.
You are not alone in the occasional 300bps brain and 56K fingers department--I assure you...
Haha, well put, OPNLguy! Mr Spaceman, I do the same thing. Apology accepted.
So, once the reverser handles are deployed, the throttles are moved forward as usual to increase reverse thrust? I would assume so. Unlike Airbus, Boeing doesn't have a marked "reverse area" on the throttle quadrant.
CanadianNorth From Canada, joined Aug 2002, 3377 posts, RR: 9 Reply 8, posted (9 years 9 months 2 days 21 hours ago) and read 3832 times:
Gearup... The first time one of my aunts was on a plane she saw the reverse action there going on and she went as green as a plant, although i am reasonably amused by all the parts shifting around followed by the powerful roar and surprisingly fast loss of speed!
DeltaGuy From , joined Dec 1969, posts, RR: Reply 12, posted (9 years 9 months 2 days 17 hours ago) and read 3714 times:
The arming before landing is the Autospoilers...done by sliding the lever (outboard, to port of the thrust levers that AJ pictured) Those are deployed by weight on gear (on the MD-88 at least). The reversers, as said, are deployed with the levers fwd of the throttles.
Autobrakes are another armed feature...but that's not totally reverser dependent
Dc10hound From United States of America, joined Dec 2000, 463 posts, RR: 6 Reply 13, posted (9 years 9 months 2 days 17 hours ago) and read 3705 times:
On the AAL B757, the ground spoilers will be deployed automatically when reverse thrust is selected, whether Auto Speedbrakes are armed or not. I think it's actually a function for RTO...
The only way to deploy the reversers is for the crew to manually pull the levers to the interlock. As mentioned previously, increased thrust is selected by continuing to pull the T/R levers past the interlock.
"Eagles soar. But weasels never get sucked into jet intakes.."
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 69 Reply 14, posted (9 years 9 months 2 days 8 hours ago) and read 3657 times:
There are two common types of reverser handles. One is a separate reverser handle mounted on a thrust lever. (Like the B-767 shown) The other is where the thrust lever itself moves aft of idle into the reversing range. (Newer Airbus)
On the Boeing type, the handle cannot be raised to the reverse postition if the thrust levers are forward of idle. Also the thrust lever cannot be moved forward of idle with the reverser handle raised. On the Airbus types that does not apply since the thrust lever itself must be moved aft of idle, but there is a small lockout lever on the forward side of the thrust lever that must be lifted in order to move the lever aft of the idle positon.
On either type the engines are at idle just on each side of the reverser interlock. Increasing reverse thrust requires pulling the levers farther aft (Airbus) or raising them higher (Boeing and McDoug) which is sort of aft or instinctively feels like aft travel.
The behind the scenes reverse interlocks that have been discussed in other replies above are found on most newer airliners but some of the early ones could be reversed in flight if you were feeling sporty. I believe that two engines in reverse idle was a speedbrake mode in the DC-8. Anyone confirm that?
Also, I think it has been cleared up already but I am not sure there are any T/Rs that can be "armed" prior to touchdown. Not necessary to take any action with cabin pressure either. Most modern systems schedule the cabin down to zero differential pressure (approximately) just before touchdown, and drive the outflow valves full open on ground shift anyway.
Last, as has been posted here before, thrust reversers are not the big factor in stopping the airplane. The shake the plane and make lots of noise but stopping with T/Rs alone would take five times as much runway as stopping with brakes alone. In fact ground spoilers are more important to getting stopped than T/Rs are because they transfer the weight to the wheels a lot faster which makes wheel braking possible.
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AC_A340 From Canada, joined Sep 1999, 2251 posts, RR: 1 Reply 19, posted (9 years 7 months 3 weeks 22 hours ago) and read 3248 times:
On the CRJ, the thrust reversers are like on boeing products, with weight on wheels and thrust levers at idle, you can move the reverse levers up and 14th stage bleed air (on -200 series, -700 series is hydraulic) opens the thrust reverser doors and then you can pull the thrust levers to whatever reverse position needed. They also need to be retracted by about 60 knots.
The spoilers and everything else are automatic. If the GLD (Ground Lift Dump) is armed, when the aircraft touches down, and the thrust levers are at idle, and there is a certain wheel speed (among other things) all of the spoilers and spoilerons deploy. They also retract automatically when the aircraft is slow enough.