Quick pre-takeoff gear hydraulic check
 

THE ULTIMATE 337 MULTI CHECK RIDE

Many moons ago, just after I bought my 'thrasher, I had a gear hydraulic line fail on my multi-engine check ride in 100F heat with an FAA inspector on board in back.

Nothing better than hearing on your multi-engine checkride in your new airplane with an FAA inspector in back,

"As per regulation XYZ, check ride is terminated, prepare for crash landing."

Back then FSDO inspectors had to go on random inspections, and I am sure to this day that fellow thought, "And I had to pick this one!"

UPGRADED LINES

BACK then I had ALL of the lines replaced with fancy 1) MIL spec 2) teflon-lined 3) metal-shielded lines. My understanding was the teflon-lined stuff doesn't break down internally like regular lines, and the metal shield helps them from 'ballooning' with each cycle, as well as mechanical protection.

My most recent upgrade a few years back was to switch them ALL again to 1) MIL spec teflon lined 3) metal shielded AND 4) flame proofed (orange stuff). My understanding the flame-proof stuff also protects them from thermal degradation from engine heat.

Suffice to say, that check ride got my attention.

=========================
PRELIGHT QUICK CHECK

Studying the hydraulics (hey, I'm a nerd, and maybe a bit of an idiot savant), I came up with a quick procedure to check the integrity of the hydraulic system before takeoff.

ON GROUND GEAR CHECK PROCEDURE

1. Scary thought it may sound, while taxiing

Cycle the gear handle down from DOWN-LOCKED to DOWN,
as if you are putting the gear down.

This pressurizes the whole system through its cycles
and returns the gear handle to DOWN LOCKED position

2. If the system is low on juice, the time to cycle increases.
I have dual hydraulic pumps.
This cycle in summer can be around 4 secs, in winter maybe 6 secs.
At around 9 secs stop and refill the hydraulic reservoir

3. If there is a leak anywhere, or any other problem,
the system won't be able to get to the full pressure
and it wont be able to push the handle back to DOWN-LOCKED.

Better to know on the ground than to discover in the air.

Standard procedure on the Piper Navajo and Cheyenne's. It's on the checklist before takeoff and before landing. Nothing new but Cessna never caught on to the idea. It's not a bad idea but I only do it about every 4-6 flights. Seems redundant to do every flight when you really know the airplane.

The procedure checks each hydraulic pump also. On start up you check the first engine started to be sure that pump is producing and on shut down you turn off that engine you checked on startup first so you can check the opposite pump before shutting down this engine.

Piper, they do things simple compared to Cessna. Cessna changed things every year they built the Skymaster. Once Piper had a system they used it throughout many years of different aircraft. Not saying Cessna was wrong, just different. They did sell more manuals that way too.