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Musketeer Split Flap Event

Mark Smith

VH-DYA

Melbourne Australia.

Reprinted by permission for the purpose of pilot education

As I sit and write this my hands are still shaking. I've had failures in a variety of aircraft types but none have been as scary, or as potentially dangerous, as what happened this afternoon as my child bride was landing our Beechcraft Musketeer Super Custom III.

All was well with the world after we'd enjoyed a nice hour-plus flight around Port Phillip Bay. It has been one of those severe clear days with light winds and smooth air. Large build-ups over the Divide kept us from our original plan of heading up to Echuca for the day. Plan B was to fly around the bay and drop in at Tyabb for a coffee. However, approaching Tyabb we heard an aircraft was stuck on the runway due to its tyre rolling off the rim, so we decided to head home. Lucky for us we did!

Turning base at Point Cook [my wife] dropped one stage of flap and nailed 80 knots like the pro she is while I enjoyed the view. Mid base another stage came down, followed quickly by the final stage [full flaps] as she turned final. Then all hell broke loose.

A loud bang was followed by an uncommanded, severe roll to the right and a yaw to the left. I looked out and saw the left flap fully down and the right flap only partially down. I dumped the flaps thinking they would retract.  Only the right flap came up. The left was still fully down.

Time seemed to slow down. I fully expected the aircraft to quickly roll over. Everything after that was a matter of instinct. I took over control and had to apply full left aileron and half right rudder to maintain something resembling level flight. The control wheel was vertical!! Thankfully I've drilled my wife to always fly her approaches slightly high when you have big runways, so I had heaps of height and therefore heaps of energy. I was more or less lined up with the grass next to the runway. Our airfield is a military base that dates back to 1916. It still is an all over airfield [all a solid landing surface—ed].

I pointed the nose at the ground, applied power and held 95 knots all the way down fearing that slowing down too much would cut down my control effectiveness. I knew that one wing would stall way before the other and that the resulting roll would be unrecoverable. Flap extension speed on the Musketeer is 100 knots so I knew I wasn’t in danger of exceeding that speed and potentially causing another failure.

The plan was to hold off a foot above the grass and let it land, using a combination of brake and the grass to slow down. My wife warned me about an aircraft that was holding for takeoff. She was concerned I was going to land on it! I’d seen it and was sure I was going to fly right on over. I did!

At round 80 knots the aircraft rolled to the right and landed on that wheel first. No amount of aileron could hold that wing up as the speed decayed. However, being only a matter of a few inches above the grass, the other wheels quickly landed as well.  To say I was relieved would be an understatement. It was only after we had shut down that the full gravity of what had happened hit me.

What really scares me is how my wife would have handled it if I hadn't been there. I have quite a few hours on a variety of types including a fair bit of aerobating, so I wasn't afraid to use full control inputs. I’ve spent time in simulators practicing all sorts of failures, including asymmetric flap deployments.

I also think we were lucky to have full flap down as the drag component inducing yaw to the left probably helped lessen the roll to the right. If it had jammed at second stage  when the flap is generating much more lift than drag then it might have been a different story.

It’s also lucky this didn’t happen while trying to land on a narrower airfield. My ability to maneuver was severely limited and I doubt I could have got into a small, narrow strip like Tyabb. Flying back to home base wouldn’t have been an option as I would have been loath to fly over populated areas with such a problem.

The cause was the failure of the inboard hinge on the right flap due to corrosion on the ribs holding the hinge. I think it may have been damaged by someone standing on the flap as they exited the aircraft as well.  It’s a known weak spot in our aircraft, but the AD covering this was supposed to have been done two years previously and wasn’t due [again] until the next annual in a year.

When the hinge failed it allowed the flap to slide back. When I retracted the flaps, slipstream pushed  the right flap up but the actuating rod was over centre, not allowing the left flap to retract. The engineer [mechanic—ed.] is going to come over next week and take both flaps off. I want both pulled down, inspected and rebuilt!

 

So what can we learn?  

During the emergency I might have  retracted the flaps too quickly. My reasoning was that I wasn’t sure how long we could maintain control with the flaps deployed the way they had, and I expected they’d pop back up together.  I certainly didn’t expect to make the problem worse by retracting them.

I asked my wife how she would have handled the problem had she been solo. She just shrugged. It’s hard to become a test pilot with 140 hours!

Apart from that the only words of wisdom I can impart are...spend time thinking about all possible emergencies and how you'll handle them. Talk to instructors and other pilots about unusual emergencies they may have had. Read everything you can about problems people have survived. Rehearse these scenarios sitting in the aircraft. Where do my hands go, what do I turn on or off, who do I talk to and how do I handle the passengers? Think about the problems you believe will never happen…They are the ones with the potential to kill you!  Right through my aviation career I've spent time with my eyes closed imagining what I'd do in a myriad of nasty situations.

Finally, when I realized I had an asymmetric problem the words of my first twin instructor came to mind...In any asymmetric situation speed is your friend!!!