***Flight Control Problems***Urgent******

[AIRFRAMER]

We have a rudder vibration that is felt throughout the full movement of actuation. We troubleshot it down to (or what we think is the rudder control output shaft on the rudder boost package.) The non adjustable linkage from the boost package to the rudder bell crank. There is obvious wear on the bearings that are in the linkage. We canned linkage from another a/c and found that linkage to be bad also. Today we have the same gripe on another a/c during preflight. Exact same symptoms exist as the other two a/c.

Continued.....I am curious if you have had this problem before and you maybe you might know another probable cause? When running through the rudder actuation, you can feel the gripe in the rudder pedals. When you run through the movement of the rudder in the hell hole you can visually see that there is play in the bearings when actuating rudder. There doesn't appear to be any discrepancies in the cage of the boost package. When actuating the rudder you can't feel any vibration in the hydraulic section of the boost package. You can feel the vibe throughout the rest of the boost package including the cage and connecting arm. This gripe was discovered on detachment on A/C 00 (which is one of the three a/c that is currently down). The Airframes CDQAR changed the booster package, and the aircraft went on FCF and pilot reported it good. The plane flew back to Kadena Japan. The plane flew several times and aircraft was up and up. On preflight yesterday 11/21/2006 there was a preflight gripe of rudder pedal vibration. We troubleshot the gripe down to the worn bearings on the rudder booster package output control linkage (non adjustable fixed lollypops). The bearings were worn and need to be replaced. We canned the arm from our hanger queen and discovered that the arm we had canned had bad bearings also. We went ahead and installed the canned arm to check and see if the gripe would stay the same, change, or fix the problem. The arm we canned changes the gripe. Instead of getting vibration in both directions like the previous rod, we only got vibration in one direction and you could visually see that there was play in the lollypop on the side that connected to the rudder bell crank. The bearing on the other end of the connecting rod has minimal wear on it. I believe that’s why you only get movement in one direction. We currently have to control rods on order. Today 11/22/2006 we got a preflight gripe on A/C 000. The gripe was vibration coming from the rudder pedals. We inspected and troubleshot the gripe and all symptoms were exactly the same as the two previous a/c. You could feel in the pedals and once you inspected it in the hell hole you could feel and see the vibration in the boost package assembly. You couldn’t feel it in the hydraulic section of the package. Throughout all three planes, all gripes feel the same way during movement, sight, and feel. The only thing is that during movement, sight, and feeling with the rudder system in boost off/out (boost handle pulled out) you don’t feel any vibration in any part of the system. I would really like to make sure that there’s nothing I am missing. I ask because it is odd, that three planes with the exact same discrepancy just went down in the last two days. If you could please lend me your technical knowledge it would be greatly appreciated. A/C's are a Navy P3C-Orion

 

[FieldTeam]

I would think you are on the right track. The probable reason you don't feel the vibe in non powered mode is that the rudder PCU is not actuated when the rudder is moved manually, so there is no (or less) friction/binding of the worn bearings on the PCU rod end. Once the PCU is actuated, the actuator grinds on the worn bearing causing the vibration to be felt.
The rudder takes a heck of a beating. You should contact engineering or MDR the parts to see if this is a fleet wide problem needing improved components.

As far as seeing this on three aircraft in the same time period, I found that once one pilot talks to the other pilots about the vibration (or whatever) then all the pilots start to look MUCH COLSER at the same thing. Your problem could have been there for a while and is just now being reported. This I have experienced first hand on several different occasions and problems.

 

[plasgears]

This vibe has been associated with accum ice in the control surfaces. Has there been a change in design beefing up the rudder gage or structure?

Early experience with vibrating controls led to lack of damping, accum unwanted mass, and increased clearances. A limber rudder structure beyond the control horn can vibrate, too.

 

[WKTaylor]

Airframer...

If You have ANY EE-EL system interface with the mechanical system, then suggest You check quality of electrical power out-put and electrical signal quality. "Dirty" power or poor signal qlty WILL influence operation of many EE-EL components... that "bench-check-good" as black-boxes.

Poor EE-EL may be due to dozens of factors including:

Corroded pins/contacts in connectors, CBs, switches, etc..

Faulty grounds [too high resistance, loose, etc].

Faulty AC/DC generators.

Faulty electrical power syncronizers or rectifiers [IE to make X-Hz steady out-put from multiple engine AC generators].

Loose connections, signal-inductance between/across adjacent wires [especially high-power wires], and damaged-wires within a wire-harness are also possible sources.

Etc...

PS: we had an acft that departed Kadena for US that lost 7-of-8 generators in-bound to AK... due to corrosion issues with wiring/connectors and a couple of ground-points. Needless-to-say the autopilot and trim systems experience bizarre excursions and had to be shut-down.

NOTE: I was at Kadena from 1990--1998. Climate caused many unusual/bizare mechanical and electrical problems.



Regards, Wil Taylor

 

[bsmith123]

I'm not that familiar with your aircraft but I am familiar with finding a part bad when I was trying to cann it! :}

Usually in a situation like this we would inspect 10 percent of our fleet and depending on the findings institute a one time inspection.

Sound like the worn bearing issue may be causing your sysmptom but are the bearings wearing prematurely? Check the A/C history and see if they were replaced before--if they have been replaced too often then the problem lies elsewhere. It could also be that you have accumulated enough hours/cycles for them to wear out and you will see it a lot on aircraft of similar hours. Those spikes happen all the time.

As long as bearing replacement cures the problem and all the ops checks are good I'd do the one-time replace the bad bearings and monitor the jets after that.


Save all the bad bearings and see if you can get an engineer to examine them for the type of wear.

Best of luck with the problem

 

[KENAT]

Has anything changed in what you've been doing with the A/C. (That's a rhetorical question, I suspect sharing that info might be a security problem).

If you've been carrying different loads, especially externally, or flying different flight profiles etc this may be causing different aerodynamic loading on the rudder which in turn may be causing the problem.

Just an idea.

bsmith123 P3 are turboprops not jets, basically a militarized Electra if I recall correctly.