LR60 Crash KCAE: Another Angle

[PURPLEHAZE21]

We Are All Human....

 

[400A]

LRvsH25B. My opinion is a little more complicated than yours. First of all I think your F/O jumped the gun. Second , did you brief that you wanted those call outs, or was it possibly company procedure? If you as a PIC knew you were landing on a slick runway you should (and may have) brief what call outs you want. If you had then yes sir, she blew it. I am not second guessing you at all.

I always announce an abort. In most of the planes I have flown, the PM does not have much to do. In the Beechjet, all he had to do as speed brakes, In the Hawker if I want lift dump, he is going to have to give me flaps 45. This is Really critical at night in my opinion. Remember the EAL 727 that ran over the B100 at night?


As far as the speed call outs, I certainly
understand why you wanted them on a slick runway. Our standard is 80kts (for the Tiller) and 60kts (for the T/R's) My personal belief is that you can make to many call outs. I call it rattling. I want previously briefed or standard call outs. Other than those I want a call out if something is "off" or I have missed something. If I am flying a approach to minimums, and someone never shuts up all the way down final, I may not catch the 1 call out that I needed. Final is not in my opinion the place for a non stop stream of call outs from the PM. If I have the approach wired, do not distract me other than standard call outs. If I am centered on Loc/GS and stable on speed, I probably know that.

Just my opinion, not bashing anyone.


As far as the accident, I believe because of how far it traveled even after the gear was gone, that for some reason that bird was still making power. weather it was the previously mentioned T/R piggyback issue, FADEC issue or something else. I have know clue and do not know the 60.

 

[bizjet800]

This is actually a common misconception. When metal contacts the runway at high speed (like with a blown tire or a single main gear failure) there is actually less friction then when a tire contacts the runway.

That might be true in the lab, but what about when there is rubber and steel belts flying around in every direction? And what about when the wheel decides to disintegrate? What speed does that happen? And you can't be certain in this, or any case. We can all MMQB this situation, but like others have said, I find it hard to believe that this plane didn't coast to a stop after accelerating to only 80 kts.

 

[~~~^~~~]

What is the "T/R Piggyback issue?"

Do the Lear T/R have a handle forward of the thrust levers that is locked out when the airplane senses that it is airborne, or some other arrangement?

What I'm really wondering, is can you get the TR handle up and in use, while the TR are actually stowed because the squat switch is damaged resulting in a false aircraft in flight signal.

 

[Basil]

What I'm really wondering, is can you get the TR handle up and in use, while the TR are actually stowed because the squat switch is damaged resulting in a false aircraft in flight signal.

If I read your question correctly, the answer is yes and no depending on the order of events. Keep in mind that the LR-60 requires that BOTH squat switches must be in the ground mode and both thrust levers must be at idle in order to ARM the T/Rs. When BOTH Thrust Reversers indicate that they are DEPLOYED, a solenoid actuated balk in the thrust lever quadrant is released and the piggybacks are free to move fullly aft beyond the idle position and command additional thrust from the FADEC.

Scenario #1 (all LR-60s)
-Aircraft on ground
-Squat Switch (either or both) damaged and now in air mode
-Thrust Levers to Idle
-No ARM for either T/R
-Piggybacks could be moved slightly aft to idle deploy position but no farther due to solenoid balk
-No movement of T/Rs and no thrust increase

Scenario #2 (pre s/n 276 and no SB 60-78-7)
-Aircraft on ground
-Thrust Levers to Idle
-Both T/Rs ARM
-Piggybacks to Idle Deploy
-FADEC moves N1 Bugs to limit available N1 based airspeed, etc
-T/Rs deploy
-Solenoid Balk released
-Squat Switch damaged=Air Mode
-T/Rs Autostow, FADEC commands Idle regardless of Thrust Lever or Piggyback position
-Solenoid Balk re-engaged
-after T/Rs stow, FADEC positions N1 bugs to Max Takeoff N1
-During the entire sequence, Thrust was at Idle because the piggybacks were never pulled aft of the idle deploy position

Scenario #3 (pre s/n 276 and no SB 60-78-7)
-Aircraft on ground
-Thrust Levers-Idle
-Both T/Rs ARM
-Piggybacks pulled to Idle Deploy
-FADEC repositions N1 bugs to Reverse schedule
-T/Rs Deploy
-Solenoid Balk Release
-Piggybacks pulled fully aft (beyond balk)
-Thrust increases to max reverse allowed by FADEC
-Squat Switch damaged=Air mode
-FADEC commands Idle and T/Rs autostow
-Engines reduce thrust to idle
-Solenoid Balk re-engages, but piggybacks are already aft of balk
-After T/Rs stow, FADEC repositions N1 bugs to computed Takeoff N1.
-Engines accelerate toward Takeoff N1, though may not actually achieve it. I suspect that you could expect around 90% N1. Note the the FADEC cannot distinguish between Thrust Lever versus Piggyback movement. The FADEC receives an input from a rotary switch in the thrust lever quadrant which is moved by both the thrust lever and piggybacks.

Scenario #4 (s/n 276-ish and up or aircraft with SB 60-78-7 [includes N999LJ based on s/n])
-Aircraft on ground
-Thrust Levers-Idle
-Both T/Rs ARM
-Piggybacks pulled to Idle Deploy
-FADEC repositions N1 bugs to Reverse schedule
-T/Rs Deploy
-Solenoid Balk Release
-Piggybacks pulled fully aft (beyond balk)
-Thrust increases to max reverse allowed by FADEC
-Squat Switch damaged=Air mode
-Thrust Reversers are receiving an input from wheel speed detect box (originally used for Autospoilers) and disregard the squat switch air mode input, thereby remaining deployed. This was a result of the N1DC accident in which the T/Rs stowed after the aircraft struck deer on rwy and damaged squat switch, creating a "scenario #3" event.

I think that what doomed N999LJ was that somehow the wheels locked up, thereby nullifying the protection that the wheel speed detect box provides to the T/Rs to prevent on-ground autostow when the wheels are spinning. This lockup could have been caused by the loss of antiskid associated with the failure of a squat switch or the loss of antiskid from use of emergency brakes. This would effectively make N999LJ a "Scenario #3" aircraft.

 

[~~~^~~~]

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:

---------------------------------------------------------------------------------------
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....

 

[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.