rfresh
B-777
- Joined
- Nov 17, 2005
- Posts
- 161
I read the initial NTSB report on this accident. They confirmed that there was an 18 second delay upon touch down from the time the pilot tried to activate the reversers until the engines actually went into reverse thrust!! Landing on a snow and ice covered runway, at night, in a snow storm, and having to wait 18 seconds for the reversers to work is a life time!!
I used to instruct on the B-727 and B-737 for a major airline. Normally, when the pilot raises up the reverser levers, they come up about an inch and then stop - there is a physical interlocking device that stops the levers from being lifted up any higher at that point.
This is called the 'detent' position. It's purpose to to send an 'unlock' and then 'deploy' signal to the cowling doors on the engines and cause the reverser doors to deploy by sliding aft on the outside of the engines. This will expose those reverser deflector vanes you can see when landing if your sitting in a pax seat next to an engine.
Once the reverser doors have slid fully aft and have locked into the reverse position, that interlocking pin in the clockpit is pulled out of the way and *now* the pilot can continue pulling the reverser levers up and aft to increase reverse thrust action. This normally takes about 1 to 2 seconds max. The pilot not flying (PNF) then calls 'two green lights' so the pilot flying (PF) knows he now has full reverse thrust capability. When the reverser doors unlock there are two amber 'unlock' lights that illuminate...when the doors slide fully aft and lock in reverse thrust position, two green lights illuminate indicating the doors have position properly and the pilot can now continue to pull up and aft for reverse thrust (the green lights also mean then interlocking pin is now out of the way of the levers).
The reverser levers once past the unlocking detent actually just work as thrust levers...pull up and aft and you'll increase engine thrust which pushes more air out the reverser vanes deflecting much of the thrust forward. My private pilot friends who have not piloted jets are surprised when I tell them the engine don't actually 'reverse' their rotation to generate reverse thrust on landing!
Anyway, an 18 second delay in getting reverse thrust on that SWA 737 tells me the reverser doors for some reason didn't slide fully aft to release that interlocking pin device up in the cockpit. The pilot can keep pulling up and aft on the reverser levers all they want but they will never break that steel interlocking pin. In that initial detent position, once the reverser doors have slid fully aft, the engine are in idle reverse thrust. So, unless you can continue to lift the levers up and aft, you won't get any reverse thrust to speak of.
In summary, from reading the initial NTSB report, it does sound to me like there was some mechanical problem with the reversers going into the reverse thrust mode for some reason.
I used to instruct on the B-727 and B-737 for a major airline. Normally, when the pilot raises up the reverser levers, they come up about an inch and then stop - there is a physical interlocking device that stops the levers from being lifted up any higher at that point.
This is called the 'detent' position. It's purpose to to send an 'unlock' and then 'deploy' signal to the cowling doors on the engines and cause the reverser doors to deploy by sliding aft on the outside of the engines. This will expose those reverser deflector vanes you can see when landing if your sitting in a pax seat next to an engine.
Once the reverser doors have slid fully aft and have locked into the reverse position, that interlocking pin in the clockpit is pulled out of the way and *now* the pilot can continue pulling the reverser levers up and aft to increase reverse thrust action. This normally takes about 1 to 2 seconds max. The pilot not flying (PNF) then calls 'two green lights' so the pilot flying (PF) knows he now has full reverse thrust capability. When the reverser doors unlock there are two amber 'unlock' lights that illuminate...when the doors slide fully aft and lock in reverse thrust position, two green lights illuminate indicating the doors have position properly and the pilot can now continue to pull up and aft for reverse thrust (the green lights also mean then interlocking pin is now out of the way of the levers).
The reverser levers once past the unlocking detent actually just work as thrust levers...pull up and aft and you'll increase engine thrust which pushes more air out the reverser vanes deflecting much of the thrust forward. My private pilot friends who have not piloted jets are surprised when I tell them the engine don't actually 'reverse' their rotation to generate reverse thrust on landing!
Anyway, an 18 second delay in getting reverse thrust on that SWA 737 tells me the reverser doors for some reason didn't slide fully aft to release that interlocking pin device up in the cockpit. The pilot can keep pulling up and aft on the reverser levers all they want but they will never break that steel interlocking pin. In that initial detent position, once the reverser doors have slid fully aft, the engine are in idle reverse thrust. So, unless you can continue to lift the levers up and aft, you won't get any reverse thrust to speak of.
In summary, from reading the initial NTSB report, it does sound to me like there was some mechanical problem with the reversers going into the reverse thrust mode for some reason.
