bombinha

I have never worked for Boeing but I do know from friends that they went into design overload after the Lauda Air incident to redesign the reverser systems.

I'm surprised the PW4000 reverser was certified for in-flight deployment in the first place - may be an ex Boeing person could clue us in on this.

I agree on the "no perfect system" since the only truely safe aircraft is the one that never flies (even then you could trip over the landing gear I suppose :D )

The science is to produce a system that has a probability of inadvertant deployment so low as to be acceptable to our good friends at the FAA.

Going back to certification by controllability, the TR has proven by testing and/or analysis that it is structurally adequate during deployment at certain prescribed airspeeds and power settings, maybe the Lauda Air TR was certified using system redundancy - that is pure speculation on my part.

I've been away from reversers for a while but the probability numbers (for inadvertant deployment) generated by the system Failure Modes and Effect Analysis (FMEA) need to be extremely small.

I guess what I am rambling on about is that we endeavor to reduce/mitigate the risk to an acceptable level....by definition it cannot be eliminated.

Apologies for any spelling errors - I'm asn engineer, we are not supposed to be able to spell ;)

The Trident could use reversers from any altitude, see Arthur Whitlocks book "Behind the Cockpit Door", for a memorable war story about an emergency descent into PMI after a pax cut her fingertip off in the loo door.

They got down safely and the finger was repaired successfully.

When I tried the same in the sim, the RoD was about 15Kfpm.

rubik,

My Boeing 737 Operations Manual in the section for Engines, APU (page 7.20.8 paragraph 3) states quite clearly: 'The thrust reverser can be deployed when either radio altimeter senses less than 10 feet altitude, or when the air/ground safety sensor is in the ground mode. Movement of the reverse thrust levers is mechanically restricted until the forward thrust levers are in the idle position'. There's no and in there (or even AND).

Undesirable it may be, but possible.

Flap5

Just to show my ignorance, does the rad alt measure from the bottom of the fuselage? So would less than 10 feet mean that the gear is in contact with the ground or just above it?

Is the "air/ground sensor" a posh phrase for a squat switch?

My knowledge turns to "general" at best, beyond the firewall ;)

Thanks in advance for the answers.

The transmitter and receiver for the radalt is on the underside of the fuselage. So at 10 feet radalt the wheels are just above the runway. The main danger of this in practical terms is if you had cracked the reversers open in the flare, by raising the reverse levers a bit too soon, and then initiated a go around. This could happen on a low visibility approach if you found yourself close to the edge of the runway or with a runway incursion as you are about to touch down. The reversers should stow but if the system stays in the ground mode they will not and then you have a dangerous situation.

Yes air/ground safety sensor is american for squat switch (why use two words when four will do!). :D