Lear35A Thrust Reverser ARM Lights

[ark 1,290]

In both the sim and real world the Lear35A thrust reverser ARM lights don't come on until the a/c is on the runway with weight on the wheels. This seems strange to me because you would think the pilots would like to know the thrust reversers are successfully armed before actually trying to stop on the runway. Why not have the ARM lights come on when the ARMing switches are activated on final approach (indicating a functioning thrust reverser system), and simply require weight on the wheels before the thrust reversers can actually deploy? There must be a good reason for the system working as it does, but I can't think what it might be.

Ideas?

Thx,

Al

[bpcw001 22]

As I understand it, the ARM lights are not meant to reflect the position of the ARM switches, but indicate that the thrust reversers are now ready to be engaged when pulling back on the levers.

 

Of course, this should never be possible while airborne, so that the lights come on only as soon as weight on weels is detected makes perfect sense to me.

 

So, as a pilot, is is a three step process:

 

1. put switches to ARM position, verify by switch position (not ARM lights)

2. on touchdown, verify reversers are ready by examining ARM lights

3. engage reversers

[bpcw001 22]

Another reason I could think of:

 

If the ARM lights were just to show that the reverser system is basically operational but thrust reversers would actually only deploy on the ground, you could never be sure that they could also be engaged while in the air.

This would require two monitoring systems: 1. Reverser system operational, 2. Reverser system inactive (while in the air) or active (on the ground)

 

With the system as it is, the ARM lights stay off in the air. Would they come on, it could indicate a malfunction in the weight-on-wheels detection system, thus requiring special care not to engage the reversers when airborne.

Given the incidents with accidentally engaging reverse thrust systems in the air (especially at the time when the Lear's were fitted with them), the designers might have thought that with only one monitoring system in place, realizing only on the ground that the reversers are inop is far more preferrable to having an in-the-air reverse thrust incident.

[CW46 101]

Link to applicable Dee Howard TR-4000 thrust reversers from Learjet 35 pilot training manual.

 

https://www.dropbox.com/s/wls6cxfdmtpqwqh/TR-4000.pdf?dl=0

[bpcw001 22]

Thanks for the link to the TR-4000 manual section.

 

So, as far as I understand, if you want to check for operational reversers during approach in flight, you need to use the "test" position of the switches.

[ark 1,290]

Good info, thanks very much Gary.

Al

[rgriffi163 0]

How do you engage the reversers once they are armed and weight on the wheels ?

[ark 1,290]

I have a Saitek throttle quadrant. There is a switch at the bottom of the throttle lever range, below idle,  which I have set up in FSUIPC4 to activate the Throttle Decr control 'with repeat while held', which activates the thrust reversers if they are armed. When the lever is moved out of the switch position, the control Throttle Cut is activated. So bottom line, a switch is used to activate thrust reverse.

Al