LR60 Crash KCAE: Another Angle

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Thank you for your explanation.

 

[ultrarunner]

I want Basil teaching my next recurrent!

 

[Basil]

I want Basil teaching my next recurrent!

Thanks for that. The truth is that I didn't fully understand the way that the FADEC would react until I dug into various manuals and even conducted a few experiments in our -60. The FADEC only looks at the actual T/R position for stowed or deployed information, not the piggybacks, so it only knows what is happening, not what the pilot wants. If the squat switch is in the ground mode and the T/R is stowed, the FADEC is on the forward thrust schedule, and if the T/R is deployed, the FADEC is on the reverse schedule, all regardless of piggyback position.

When viewed from the perspective of an airborne T/R deployment, the system works great: Idle power, Autostow, then Forward thrust, all with no pilot action. Unfortunately, this logic can be a disaster on the ground if a single squat switched fails after you've deployed the T/Rs beyond idle, hence the wheel speed input Service Bulletin.

LR-60 pilots need to grasp this as the reasoning behind the following Memory Item quoted from the AFM:

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INADVERTENT STOW OF THRUST REVERSER AFTER A CREW-COMMANDED DEPLOYMENT​

1. Maintain control with rudder, aileron, nose-wheel steering, and brakes.​

2. Both Thrust Reverser Levers — Stow.​

Note => Failure to move the thrust reverser levers to stow will result in forward thrust ranging from idle to near takeoff power, depending upon the position of the thrust reverser levers.​

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It's not my place to publish the "probable cause" for the CAE accident, but I feel that some unfortunate combination of events may have conspired to create the previously mentioned scenario #3. If there is one way that we can honor the loss of the pilots and passengers aboard N999LJ, perhaps it can best be done by better understanding our jet and avoiding a similar accident in the future....

 

[AviateYou]

Thanks for that. The truth is that I didn't fully understand the way that the FADEC would react until I dug into various manuals and even conducted a few experiments in our -60. The FADEC only looks at the actual T/R position for stowed or deployed information, not the piggybacks, so it only knows what is happening, not what the pilot wants. If the squat switch is in the ground mode and the T/R is stowed, the FADEC is on the forward thrust schedule, and if the T/R is deployed, the FADEC is on the reverse schedule, all regardless of piggyback position.

When viewed from the perspective of an airborne T/R deployment, the system works great: Idle power, Autostow, then Forward thrust, all with no pilot action. Unfortunately, this logic can be a disaster on the ground if a single squat switched fails after you've deployed the T/Rs beyond idle, hence the wheel speed input Service Bulletin.

LR-60 pilots need to grasp this as the reasoning behind the following Memory Item quoted from the AFM:

---------------------------------------------------------------------------------------
INADVERTENT STOW OF THRUST REVERSER AFTER A CREW-COMMANDED DEPLOYMENT​

1. Maintain control with rudder, aileron, nose-wheel steering, and brakes.​

2. Both Thrust Reverser Levers — Stow.​

Note => Failure to move the thrust reverser levers to stow will result in forward thrust ranging from idle to near takeoff power, depending upon the position of the thrust reverser levers.​

---------------------------------------------------------------------------------------

It's not my place to publish the "probable cause" for the CAE accident, but I feel that some unfortunate combination of events may have conspired to create the previously mentioned scenario #3. If there is one way that we can honor the loss of the pilots and passengers aboard N999LJ, perhaps it can best be done by better understanding our jet and avoiding a similar accident in the future....

Don't misinterpret this, I agree the more you know about systems the better, In this case I think that next time at 136 KIAS in any Lear we should just commit to flying it off the ground. In the real Learjet, I have personally landed with a blown main tire and rim that was broken in half without incident at close to MGLW. It can be done and I am grateful that we were that fortunate. On the Learjets, each one of those tires has a load capacity of of over 6000 lbs if properly inflated and in servicable condition and 3 of 4 are capable of supporting the aircraft at MGLW. The loadrating is on the tire.

 

[ultrarunner]

Aviate is spot-on. A crew has to be absolutely positively certain the airplane WILL NOT FLY, if attempting an abort anywhere NEAR V1.

And don't hesitate to use the WET V1 if you're not runway limited. Reduced-Decision-Speeds are SOP's at the airlines, and for very good reasons.

And if you haven't complied with S/B 60-78-7, get it.

 

[WTF]

Sim

For what it is worth. I just came back from recurrent and my partner and I simulated 4 blown tires 4 times, before V1 twice, at V1 and after V1. It was very violent and difficult to control initially but all 4 times we achieved rotation and climbed out.

Aircraft was at 20500lbs
8000 ft runway
300' elev

In this simulation, I can see how a crew could reject just for the fact that something MAJOR was wrong with the aircraft.

I am not saying that we duplicated what was going on but I just wanted to share what we experienced.