Prop Brake... Good, Bad??

[SRT1968]

My situation is as follows. Aircrew takes a AC,MC,C-130E,H, any of the sort, up for an FCF. I am told that in order to op ck the prop brake, local policy, no one can give me a tech data ref, but local policy is to cage the engine at 180FL. If the propeller rotates backwards it is immediately a write up requiring a flush.

OK, my argument to this is that if the FCF is op cking an emergency procedure then why is it immediately a write up at 180 knots? Especially since no airspeed is given in the -1 or FCF ck list to feather the prop at. I tend to think that if the aircraft slows as the -1 says to 160 or less to get the prop to stop counter rotating, then once the prop stops, accelerate to 200 knots and if it stays stationary then no discrepancy exists because 200 knots is top of the design limitations and should not be exceeded, which is in the -1 and FCF cklist. But it has to stop first in order for it to hold up to 200 knots, kind of like a skidding tire has less traction than one that is not sliding.

Also, to continue on with the subject of flushing. Does any one think that rotating the prop backwards, removing air/alcohol pressure from the prop brake release tool and "slamming" the brake is a good idea? Another local policy. The tech data says noting of this procedure of slamming. I agree with rotating the prop during the flushing cycle to help "slosh" it up a bit, which is not in the tech data, but I don't agree with the slamming of it. Just throwing it out there for some feedback. Thanks

Edited August 27, 2009 by SRT1968

[NATOPS1]

NAVAIR 01-75GAA-2-4

MAINTENANCE INSTRUCTIONS

(ORGANIZATIONAL)

POWER PLANT NAVY MODELS

C-130T, KC-130F, KC-130R,

KC-130T, KC-130T-30

AIRCRAFT

NOTE

The propeller brake system is unsatisfactory if there is reverse rotation with the propeller

feathered at 10,000 feet MSL and at 200 KIAS.

Step i of our flushing procedure is as follows.

The procedure may be repeated if propeller brake serviceability is not fully restored.

I guess "they" just "cycle" the prop brake and repeat the procedure....(without clearing the solvent first)

As far as the 160 or 180 knot discussion your point of view is a good one however the test is not for the emergency procedure but for the prop brake. If the brake does not hold then the EP applies, slow to 160 and increase airspeed to a point where it starts to rotate takes over... but one could say that if the EP proved successful and the aircraft accelerated to 200 and the prop brake held then it could be considered OK...

HOWEVER!!!!, As a flyer I can say if a system fails to the point whrere you need to follow a published emergency procedure then the aircraft is in a degraded condition and maintenance needs to be performed. (SO IMO I would have to write it up and get some maintenance done!!)

Edited August 27, 2009 by NATOPS1

[pjvr99]

NATOPS1 correct! T56-56 states the only check for propbrake serviceability is inflight shutdown - no rotation allowed! You can try flushing it out (followed by a ground run), then FCF again. Being ground-bound, I have no knowledge of speeds and altitudes

[Guest]

Sounds like someone needs to suggest a revision to the FCF procedure.

Edited August 27, 2009 by TalonOneTF
mixed numbers

[impact12]

Prop brakes have been a perpetual problem since we had to change brake shoes during the mid 1980's and I do not see the situation changing in the near future. We have had RR investigate the problem to see if there was anything we could do differently in overhaul to make the current brakes last longer. Although there were a couple minor improvements made, the core issue was the shoes (duh).

One thing that we did discover in the process is that the flushing procedure is questionable at best. When we looked at what actually happens when a prop brake is flushed, the most likely reason why the brake works during the subsequent FCF is because the solvent has dried out the surface of the pads, resulting in a (temporary) increase in the coefficient of friction. Although I have long suspected that the prop brake would not work again after it is fully oil soaked again, I have never been able to talk a unit into rechecking a prop brake after some time has passed. If I were at a unit I wouldn't be keen on rechecking the prop brake either because I'd be setting myself up for a RGB change.

The reason I say that the situation will not change soon is that the engineering task to redesign the brake shoes is not being funded. Problem is that the way that the engine CIP community looks at safety necessitates that the safety issue get assessed wrt non recoverable in-flight shut downs (NRIFSD) and catastrophic mishaps. As a prop brake cannot cause a NRIFSD and is highly unlikely to cause a mishap (in isolation), the prop brake does not rate very high from a safety perspective in the CIP community. The other problem is that the overwhelming majority of discrepant prop brakes are identified during FCF which, in the USAF at least, are mostly accomplished in conjunction with PDM so the problem is somewhat hidden from the field.

In summary, there really is no remedy for the current situation. Several years ago we elevated the problem thru HQ AFMC to HQ AMC and had the 4 buttons sign off on current guidance. Since then I did change the FCF guidance so that we are doing a few more FCFs in the field but O/W our hands appear to be tied.

[Steve1300]

During my AF years, I remember prop brakes being checked during FCFs and all that. The only thing I have yet to see is a prop rotate backward after shutdown. I have seen many engines shutdown in flight since retiring from the AF, and I have still not seen or heard of one rotating backward.

Are prop brakes really a problem, or it is more a matter of setting too high a standard for their testing? When all is said and done, is it still not just a matter of whether or not the prop brakes work after an in-flight shutdown?

Maybe I am just missing the point, here.

[Lkuest]

"I am told that in order to op ck the prop brake, local policy, no one can give me a tech data ref, but local policy is to cage the engine at 180FL. If the propeller rotates backwards it is immediately a write up requiring a flush."

The 1C-130E(H)-1 states that the prop brake is designed to hold up to 200 knots, but you may have to slow down to 160 knots to get it to stop. If it stops, you can speed up until it starts rotating again, then slow down, but no faster than 200 knots. If it doesn't stop rotating at 160 knots, stay at 160 knots until landing.

The FCF tech data may have an actual ops check for the prop brake, but I just want to point out that the H-1 isn't telling you how to ops check the prop brake, it's only telling you how to react to the circumstances of a propeller rotating backwards.

I've only heard of our flight engineers at Little Rock complain about 160 knots rotation. The 1C-130H-2-70FI-00-1-2 states you must ops check the prop brake in flight using T.O. 1C-130B-6CF-1. I've never read it, but I hope it'll point you in the right direction.

[Skip Davenport]

While in the 7SOS in Germany we were checking out an FE to be a FCF/FE. Now the bird we were flying was G-2-G and did not require an FCF. When we did the inflight condition lever to ground stop procedure two of the props started to go to feather -- back to run and everything was ok. Back on the ground we wrote everything up. Now this pissed off the MAC maintenance NCOIC big time! Before I could get back to Bldg 152 our squadron. The boss had already been called by the DCM raising hell about us doing an FCF on a good aircraft. He was especially upset with the inflight ground stop procedure and demanded I return to maintenance to sign of the write up as "entered-in-error". When I got to the DCM's office I was meet by him and the NCOIC. They explained to me that it was "perfectly normal and nothing was wrong the props" and I could "legally" sign them off. I said sure show me in 0020-5 how to sign them off but then I would have to write up the other two props as bad as they didn't try to go to feather. The NCOIC turned beat red and the DCM told me to "get the f$$k out of my office". Later my CC told me that I need to try to be more diplomatic with an O6 and senior NCO.

[Dave in WV]

Skip, you found an unknown problem and then they didn't want to fix it? Bad joo joo. I remember when they did away with the static feather check. Someone somewhere along the line was SUPPOSED to do the check at an unspecified time. Good idea!

[Lkuest]

The static feather check is required in the 1C-130H-2-12JG-10-2 work package 12-16-03. Basically, you are required to perform the check every time you do a 15-day prop service check.

[tacairlift]

Let me help, if my memory is correct (retired 5 years). You always want to feather the prop at 180 TAS because if the prop fails to feather, it should decouple but if doesn't decouple at 180 TAS, the blade angle should at a high enough to minimize windmilling drag and RPM's and keep thing controllable. It is also a good speed to restart the engine if the shut down went okay. If it feathers but rotates backward the brake is not working, you then speed up and slow down in an effort to seat the brake. If that doesn’t work, your done, declare an emergency and RTB. You can't restart it because you may blow the starter or gear box because of additional load caused by the backward rotating prop. You RTB at 160 TAS (slow) because the gear box is moving but is not getting lubrication, the pumps are going backward. As you slow down for approach, have the load tell you when it stops rotating and note the speed for Mx. I think about half of the FCF's I did for engines, I came back with one rotating backwards and after Mx flushed the brake, half of those still rotated.

After rereading the origional question, let me add: The prop should never rotate backwards at less then 200 knots as designed. So if it is rotating at 180, it is still bad even if you can stop it at 160. The slowing down during the FCF to stop it is to do only that, stop it, so the gear box dosen't blow due to lack of lubrication and creating a bigger emergency. If you are able to stop it by slowing, you can then start the engine, finish the FCF and go home but the brake is still bad. During the FCF if the prop does not rotate, you accell to 200 to test the brake to see if it still holds as designed. As far as the altitude is concerned, higher is safer and is usualy based on the local area to keep the FCF away from local traffic, above the clouds, and populated areas. In addition, the brake test is done using True Airspeed (TAS), since the prop only "sees" TAS, then the altitude does not matter but you will need the high altitude during the FCF for safety and for other checks (ie. high speed flutter check). Remember to reference the correct manuals -1 and -6? for the correct procedures, my info is all from memory.

Guido

Edited September 1, 2009 by tacairlift
Added last para and disclaimer - so there

[NATOPS1]

Ours reads like this....

Shutdown at 150 KTAS ensures decoupling if propeller fails to feather.

The drag on a propeller coupled to an engine is significantly higher than a decoupled propeller; thus it is desirable to have it decouple.

150 KTAS is considered high enough to cause decoupling, but not high enough to cause excessive drag or overspeed after decoupling.

We discuss "bumping" airstart to decrease the BA to a point where it stops.....

We are talking very slow (reverse rotation)