thrust reverse isolation valve b 737 200
 

the isolation light on p5 for the thrust reverse remains on in flight,and the t/r unlock light all them are off what can be the problem?

I have had that problem, turned out to be the nose gear was not completely up and locked due to snow. This may not be your issue but may have to do with main landing gear sensors in flight.

Why not check the fim and mm thats what they are there for?!!!

The isolation light tells you if the TR isolation valve is in the incorrect position ie TR isolation valve open when in the air

chapter22, you have to define "open". ;)
The valve is de-energized in air. This mean that the valves shut off pressure to the reverser and connect the reverser hydraulic system to the system return line.

Not fully shut ie at any position away from closed either driven or stuck.

To make clear what i mean with define:
Which lines are connected in energized/de-energized situation.

A picture should help.
http://bit.ly/wupbQ6

The pressure switch is looking at the up stream hyd pressure to the thrust reverser. on the ground pressure would be expected at that point and via the air ground logic the light would be off.in the air the pressure switch should not see pressure if it does via the air ground logic the light would be on telling the crew that there was hyd pressure at the thrust reverser an unsafe situation with the possibility that if the flight crew were foolish enough to try and deploy the thrust rev in flight it may deploy. The schematic does not give the full story only the mechanical bits!!

On ground the valve is energized allowing hyd press to the thrust rev.in the air it is deenergised from memory I think this is correct only thing is with total electrical failure there would be no thrust rev which does not seem correct but can't check as do not have access to a -200 schematic! Unless the supply comes from the battery bus.

From memory, the Isolation Lt is on if the pressure in the line is above 250 psi. :cool:

t/r iso valve light
 

thanks man you help me ,the nose landing gear sensores was the cause we replace them the light remains off during flight. thanks

Glad to be of help.