Page 21 - August 2023

“The main reason for stowing the handle in the hydraulic system is that when the handle is down to floor level, it relieves the pressure in the emergency extension lines.”
opening of the nose gear doors is a little easier, since their leading edges tuck a bit into the air flowing past the nose. In the hydraulic system, those first pumps merely remove the pressure that is holding the gear up and gravity will now take over and do much of the rest. Since the relative wind helps the mains extend but hinders the nose, the mains fall to what appears to be fully extended – but they’re not locked – whereas the nose ends up at about a 45-degree angle. So it still takes close to 100 pumps on the red handle (even more than those needed in the mechanical system!) to finally get all three green
lights to come on as the locking takes place.
There is so much mechanical advantage designed into the manual ratchet device associated with the electro-mechanical system that pumping it past the point of the gear being fully down and locked could lead to damage ... probably bending an actuator rod or nose gear brace since there is no more room for further travel of the gear. Since taking even an extra half-stroke or so to stow the handle could cause damage, it’s not advisable. After all, the mechanic is going to have to jack the plane and see what’s wrong anyway, right?
The main reason for stowing the handle in the hydraulic system is that when the handle is down to floor level, it relieves the pressure in the emergency extension lines. Once the green lights come on, indicating the gear is mechanically locked in the fully down position, there is no reason to maintain the pressure there, so relieving it (1) leads to less chance of a leak developing, and (2) makes it possible for the gear to be retracted normally. (That is especially important if this was an in-flight emergency extension conducted for training purposes.) If
the pressure is not relieved before the CB is reset and the gear handle is raised, often the motor will run in excess of the 14 seconds or so that triggers the automatic shutdown, including the blowing of the Landing Gear Relay circuit breaker.
You didn’t mention it, but I am sure you know the checklist for the procedure relating to the hydraulic system also specifically states to not stow the handle and, in fact, to keep pumping it often until jacks are under the jack points, if a green light will not illuminate. The thinking here is that even if the gear actuator wasn’t moving all the way to cause the lock to function, missing it by just a bit, sufficient pressure kept in the emergency extension lines may keep the gear extended until the maintenance folks get the jacks positioned.
One last comment: If you are doing a landing gear manual extension exercise for training purposes in the electro-mechanical system – either during a training flight or while the airplane is supported on jacks for routine maintenance – sometimes you may run into a little snag when the procedure is finished and the three green lights are on. Since the procedure directed you to not stow
AUGUST 2023
KING AIR MAGAZINE • 19