gear pins - what for?

[galleypower]

Dear ppruners,

Is there anyone out there who could give me some good reasons why to install gear pins. I know there are plenty of good reasons...
.Could manouvering an unpowered aircraft without pins make the gears collapse for instance?

Thanks for your thoughts...

[john_tullamarine]

Where the situation involves a defect which might cause the normal locking mechanism to fail (or the mechanism is, itself, defective) use of pins is necessary to provide redundancy or provision for locking.

In other cases, it just makes for a good insurance against unexpected mishaps.

[Capt Claret]

galleypower

I don't know how the following incident happened but it did.

Years ago a Mohawk was having some work done in the hangar at Bundy (YBUD), preparatory to a charter flight the next day. Engineers crawling about the outside and some in the flight deck.

One engineer was lying on his back on the F/O's seat, wedged under the instrument panel doing whatever. When he pulled himself out he knocked the undercarriage lever, which some how sprang to the up position and the U/C retracted leaveing one 7 or 8 tonne aircraft sitting on it's guts in the hangar floor.

The squat switches should have prevented the retraction but didn't.

[Blacksheep]

Gear pins lock the locking mechanism in place, providing an additional layer of safety in preventing accidental gear retraction on the ground. Other parts of an aircraft have ground locks fitted for similar reasons.

The long red streamers indicate that they are in place and must be removed before flight. Otherwise they prevent intentional retraction of the gear after getting airborne. ;)

[r304ndy]

The overcentre locking feature built into all landing gears provides a primary means of inadvertent retraction. The groundlock pins provide a secondary means of safety measure.

[PAXboy]

Anything That Can Go Wrong - Will Go Wrong. :mad:

--------------------
"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.

[Blacksheep]

Anything That Can Go Wrong - Will Go WrongIncluding taking off with the lock pins still in place ;)

[brain fade]

Have a look at the geometry of those links that operate the big dangly bits with the wheels on the end.

Seriously have a wee think.

The way these links work(ie overcentre) it's quite easy for a very small force applied exactly half way along one of these links to initiate gear retraction.

Compare that wee force with the gimungous howk you'd have to apply to the actual LEG to move it.

However that wee force is all it takes to move something, that moves somethingelse, that cuts in HYD 1 und folds the whole leg right in under you!

A wee teeny pin stuck through the link (described in para 3 above) stops it all starting.

AND causes those embarrassing 'we've got a gear problem' air turnbacks.

:{

[MrBernoulli]

Blacksheep

True. But having the gear collapse/retract unintentionally is a darn sight more dangerous than being unable to get the wheels up when airborne.

Both are pretty embarrassing, though.:ok:

[FlexibleResponse]

The scene…Preflight of widebody (Old Pilot showing New Pilot the ancient art of survival which starts with a thorough and knowledgeable walkaround).

OP This is the main landing gear.
NP Wow! (sonofabitch this is a big muttha sukka!)
OP We must check that the gear pin is removed before flight. Show me where the gear pin goes.
NP (Easy question, I am think that I am getting a greasy grip on this flying business). In this hole Captain!
OP Good lad! Now tell me how the gear is extended young fella!
NP You select MLG handle down… (is this guy nuts?)
OP And how does that actuate the gear to extend?
NP Arrrrr….the electro mechanical lever doodad uses hydraulics to power the gear down?
OP Very good!
NP (Thank goodness…This guy is out to lunch…and I am gonna have to fly with him all day?).
OP Now, I think you will notice that the hydraulics are now completely un-powered, so how is the gear being prevented from folding up and crushing us to death as we do our walkaround?
NP (Holy crap! This is bad! Thinking very quickly…) Ahmm… there is some over centre doodad that creates some sort of geometric lock?
OP Very good lad, and here it is that lock just where you showed me the gear pin hole is located. Now can you tell me what is holding this over centre lock in position?
NP (Straining eyes and imaginative resources…) Might it be these little springs sir?
OP (This lad is going to be a great aviator!) I shouldn’t have to lead you around by the nose. You are going to have to work a lot harder if you want to continue a career in aviation.