Yeah Chris,

You are right that SB 739 addresses the flexible shafts. BTW, you can download 739 on the piper website.

http://www.piper.com/technical-publications-documents/

Link to the actual document if it works...

https://s3.amazonaws.com/pipercrm/Solut ... %20739.pdf

I was just saying that regardless of the failure mode, the loss of control and corresponding use of 25 degree maximum flaps, along with all POH and performance changes (none in all but the pressurized models) are addressed there.

In flying, it is nice to be able to say, "if this breaks, I won't die if I take actions a, b, c..." It just seems to me that once you put in 40 degrees of flaps (especially on a airplane with a system that you can't retract them once split) you can't say that anymore if anything fails that allows one flap to retract. Certain failure modes are common enough to warrant an AD, others are just bad luck. I realize that there are things on airplanes that if they break you are dead. But I would argue this doesn't need to be one of them.

"Flaps at 25 to stay alive"

Ailerons are neutral, but you get the idea...

Good info but this is old news and applies to many larger twins. This is the reason for keeping your hand on the flap lever in transit. If anything goes weird, immediately retract.

I do agree with not needing full flaps on final. The Navajo lands slow and short as it is.

I was aware that split flap could occur in transition, that part is old news. I did not expect catastrophic type sudden retraction, that was news to me. Also, It is pretty clear to me that the part that failed is simply worn out to the point that the ball bearings were able to come loose. No signs of any other damage. Nowhere in the AD or even in the service manual does it say to inspect that part of the transmission. I think that is newsworthy. Hell, shops might rebuild the gear part of the transmission and call it "overhauled" for all I know. This part of the transmission may be as old as the airplane. It's concerning enough to me that I have an "overhauled" transmission with 50 hours on it on my other wing that I am now going to remove and inspect for this same condition.

Pick your poison.

My 421 had extend cables that have been known to break under load. At least with a transmission and jack assembly you are most likely to experience failure in transit and have the opportunity to immediately identify the issue and retract the other side.

In the 421, if the cable breaks the flap comes up and smacks the underside of the wing. It sounds like an explosion and as the planes immediately begins to roll you think “engine failure”.

Good info for sure. Thankfully it seems very rare considering the high time commercial ops most Navajos experience.

Thanks for posting.

Good job on the recovery but seems like a failure in the inspection.
If the transmission failed at the jack screw then clearly the threads must have been completely worn. Should have been picked up during an annual inspection
I also have the 40 to 1 flap transmission which allows 40 degree flap deployment and I make sure it is fully inspected at annual.
One other thing I find unusual is using full flaps before turning towards the final approach fix. I never deploy full flaps until I'm assured of landing in case of a go around

Pretty sure I would need new seat covers, too!
Glad that everyone is still here to post today!

Mike,

You didn't read the earlier posts very carefully. You can't inspect the part of the transmission that failed in my case without removing and disassembling the transmission. To elaborate further, there is what I'll call a bypass tube that allows the ball bearings to exit one end of the transmission housing and carries them back to the other end. At the end of that tube is a tiny scoop, I'd say about 2 mm long. That little scoop disengages the ball bearings and forces them up into the tube. If that tiny piece gets worn or breaks off, the ball bearings simply fall out of the back side of the transmission housing. That tiny scoop is the one and only thing keeping the ball bearings inside the transmission. The trans mission will pass all of the inspections with only a handful of ball bearings left inside. When you lose enough balls it will fail instantly and the flap will slam up. If that happens on short final when you put that last notch in you are a yard dart. It matters not if you have your hand on the flap lever, you won't have time to retract the other flap.

FYI, the mechanical term for that ball bearing screw is a "ball screw."

Much more reliable than a jackscrew/nut arrangement, especially when properly serviced.

E