Sagging oleo PA28

[AndrewVaughan]

I fly PA28.181s at two different clubs. I have 100 hours IC but still consider myself to be a newby. I was meant to fly today with a couple of guests. The weather was fine and hot (28C). The plane had flown twice already. I completed the external inspection which was all OK but when my guest was boarding, the right oleo sagged with a clunk leaving a 5cm dispelcement difference between the right and left landing gear. We put the plane away and I messaged maintenance via the club group WhatsApp. I've since received a message from another member that the sagging is quite normal and can be rectified with a jiggle of the wing which restores the oleo to its correct displacement. He says that as long as there is still movement in the damper it's OK and that he's flown after such manipulation and had no problems.

I'm very reluctant to take the plane off the ground in these circumstances. In my view, a poorly performing oleo does not pass the external inspection criterion for the aircraft being fit to fly.

Do any forum members have a view?

[Fl1ingfrog]

This is a common problem with the PA28 series and many other types. Indeed it is true that the oleo seals can be 'sticky' and often freed as your co-member described. But you mentioned a "clunk" following the passenger standing on the wing walkway. There shouldn't be a clunk when the wing goes down unless the oleo has lost all fluid and possibly all the air and so it is bottoming. You acted wisely and possibly avoided unnecessary damage. Free advice can be costly. That old saying: 'better to be on the ground wishing you were up there than up there wishing .................etc.

[Jhieminga]

AFAIK the oleos should show approximately 11cm of the fescalised portion of the oleo under normal static load. If you load up the aircraft with fuel and passengers, it may well end up showing slightly less than that and with a sticky seal, it could act as you described. In the end, you have to be happy that the aircraft is safe for you to take up into the air, so your decision to leave it on the ground is always a good one. Somewhat older Pipers and Cessnas often have individual traits and issues that you may have to get used to. Have someone knowledgable check the aircraft and if it is safe, have them explain to you what the limits are so that you are able to judge the condition by yourself the next time.

[scifi]

Oleo Free Travel

You need to look at the Owners Manual to see how much shiney metal should be visible. For most Cessnas it is 3 inches, any less and more gas is required. The oil would be checked at the annual service.
Without any load, eg. prior to landing, the strut will be at maximum travel of 6 - 8 inches.

[EXDAC]

The PA-28 main gear has an "Achilles heel" that few operators are aware of. People assume that if the strut has lost air it must be the lower seal that the ram slides in. The PA-28 main gear struts actually have a "cylinder head" that is sealed by a O-ring. The cylinder head O-ring can only be changed by completely removing the main gear leg from the wing. The servicing hole on top of the wing allows access for normal air and oil servicing but is not large enough to remove the strut cylinder head.

I have changed this O-ring on both main gear of my 1975 PA-28-180. In both cases the O-ring fell apart when the cylinder head was removed.

Yes, pulling and replacing the main gear legs is a "fun" job!

edit to add - If either main gear bottoms out when boarding the aircraft should not be flown until the gear is serviced (opinion based on over 1,000 hours in my PA-28 and very experienced in the wing wiggle gear adjustment method).

[AndrewVaughan]

Now resolved

After a review with our mechanic and much wing jiggling, we established that the oleo was not bottoming out and that the was no lack of gas pressure. I flew the plane with no problems as have others. Thanks for all the considered advice.