Originally Posted by
tdracer
Boeing put the air/ground on the hydraulic isolation valve (HIV), .
On the MD-80 nose gear squat is used to isolate the reverser valve from main hydraulics but it leaves the reverser accumulators connected to the reverser valves. Having the main hydraulics isolated from the reverser valves by nose squat does not prevent reverser deployment. NTSB-AAR-81-16 illustrates what can happen if reversers are deployed before nose gear down. Note the procedure change that resulted from this flight test accident.
https://www.ntsb.gov/investigations/...ts/AAR8116.pdf