Skymaster down!
 

Has anyone else seen this news? I just had a google alert that sent this link. The writer of the article is pretty green about flying and aircraft.


http://www.stillwater-newspress.com/...086184217.html

Another Skymaster down today
 

This series of 2 Skymasters down within days should be of grave concern. In both instances the pilots were highly experienced (one flew for Northwest Airlines and had 30,000 hours, and the other had been a commercial pilot and flight instructor) and in one case the aircraft was state-owned and flying for a state agency (which suggests a more rigorous environment of maintenance and pre-flight checkout). And people, these were lightly loaded twin-engine Skymasters. I can see an overloaded Skymaster losing an engine at takeoff crashing, but these aircraft had a single passenger. And in the case of the state airplane witnesses saw the plane circling the fire area and then “it went straight down”.

Fuel exhaustion might explain one but not the one that "went straight down". We need to stay on top of these to find out what happened. I'm hoping a snapped flap cable (the subject of another message this morning) didn't play a part, since the aircraft that "went straight down" was not landing.

Ernie

In the second crash the plane was circling the fire and came straight down. Might have stalled it in a turn?? Whatching the fire and not paying attention to airspeed. I lost my best friend in a Yak 52 He was and instuctor and his passenger was a ex mig 29 pilot They stalled at 1200 ft in a turn and didn't have enough atlitude to recover

Stalls at low altitude are the most common cause of VFR accidents. However, flying around a fire may cause a different problem. The density alitude over a fire is insanely high...because of the temperatures. This might have agrivated a non stall condition into a stalled condition. Either way, flying around a fire isn't the smartest thing to do with an airplane.

As long as the Flap Cable question has come up, as related to these potential accidents, I would like to ask the following question to those pilots/mechanics who are familiar with the whole flap system in the 337, as follows: If a flap cable breaks, is the "other flap" usable? I.e can it be set to correspond to the "broken cable position" of the jammed flap? Granted you wouldn't have a lot of time, but if we knew the answer, we could perhaps develop a "rule of thumb" protocol.

I seem to recall on my Navajo, that if one side went, you were essentially screwed. Is this the same on our Skytrucks?

OK, here goes my understanding of the issue and how to recover. A caveat: I could be wrong and I hope others jump in here and set me straight.

When a flap cable breaks, the flap on that side snaps instantly to neutral (zero degrees). The other side remains where you set it, and the imbalance causes the aircraft to roll aggressively, especially at full flaps. The solution: with the left hand instantly apply opposite aileron (to arrest the roll) and with the right hand flip the flap handle back to zero (so the non-broken flap goes to neutral like the broken one). Bringing the flaps to neutral is critical, because for some flap settings (certainly above 2/3 and perhaps even at 1/3) there isn't sufficient aileron authority to overcome an unbalanced flap condition.

At least one pilot, on short final and with flaps deployed, was able to recover from this failure, in what was decribed as a masterful job of piloting.

On approach, part of my checklist is a reminder of what to do if a flap breaks and after setting flaps I try to keep my right hand close to the flap handle.

Ernie

Aircraft accidents aren't caused by one problem. There are a chain of events that lead up to the accident. Each link in the chain can be small, almost unnoticeable. If you can break one link in the chain good chances are you can avoid the accident.

High time and lots of experience mean nothing if the very basics are ignored or forgotten. "What? Me?, Ha, that can't happen! I'm highly experienced!"

Lots of those guys in graveyards.

I was hoping to get a response to my cause/recovery above, in part because I'd like to know for sure. Anyone who knows, one way or the other, please comment.

Ernie

The best response is have the maintenance done correctly and it doesn't become an issue ( I assume we're still talking flap cables).

Swiss Cheese
 

Ernie,

The Coast Guard (and it's Auxiliary) uses a model called Swiss Cheese to say the same thing. The example uses slices of cheese to represent occurances during a flight. If the holes in the successive slices line up, there is a corridor to an accident or incident. Any one slice being repositioned can block the corridor thereby preventing the accident.

The key is to recognize a building situation and take action to prevent it's progress.

I couldn't agree more with both of you, but Roger asked a question and I gave the best answer I had. I think some of us would still like to know: if it happens, is the information I have valid? Essentially: a) does the flap with the broken cable snap to neutral and b) will moving the flap lever to zero return the other flap to neutral and therefore remove the unbalnced forces causing the roll?

Ernie

At 1000 feet and you are quick, you may make it. At 50 feet and 80kts on short final, I doubt it.

You're only other option is to fly with the flaps left at zero.

Ernie,

I think your procedure to recover from an asymmetric flap configuration sounds logical. The only other thing I could mention would be an aggressive application of maximum power and a lowering of the nose to increase airspeed rapidly. With the sudden retraction of flaps on one side, the possibility of that wing being at or near stall would be likely which would increase the roll rate in that direction. Any increase in airspeed would at least slow the roll in the direction of the failed side assuming the yoke was turned fully in the opposite direction.

You may recall the famous crash of American 191 in 1979 with the erie photo in the Chicago Tribune just before the DC10 impacted the ground with the aircraft in excess of a 90 degree bank after an engine departed a wing on take off. It is my understanding that when the engine departed the wing it took hydraulic lines with it causing the leading edge flaps (slats) to retract obviously causing an aerodynamic imbalance. The initial rolling motion that followed was corrected by the flight crew as the airspeed was approximately 20 knots past V2. If my memory serves, the crew recognizing they had an "engine failure" followed procedure and allowed the aircraft to slow slightly to V2 which was the speed they were to fly in the event of loss of power on an engine. This slowing caused the one wing to stall and the unrecoverable roll followed. When the NTSB put flight crews in the simulator replicating the event, they were instructed to maintain the V2 plus 20 airspeed and every crew flew away to a successful outcome.

Good input. Another reason, if there is plenty of runway length, to be higher and faster than minimums on final. Altitude and speed are your friends in the flap scenario. But as Jim Stack and "Tropical" suggest, the better choice is to make sure your flap cables are inspected regularly so you never face this emergency.

Ernie

Thanks for the response that the flap would reset to "0" if the cable breaks. As for the pithy comments about maintentance, and it never happening if, blah.. blah... blah... You have got to be kidding me?

I guess based on the assurance that good maintentace is all I have to concern myself with, I will add a little useful load by throwing my Emergency POH overboard.

tks/Roger

No, I'm not kidding anyone. You can invent emergency procedures for everything.

Typically flaps aren't used at altitude but close to the ground. If your flaps go asymmetric at 50 feet on landing I doubt seriously anyone will have quick enough reactions to overcome the control forces.

Part of safe and proficient flying is having everything in order, both the pilot and the airplane. If the flaps are suspect have a mechanic go through the system and do a very thorough inspection. Unfortunately in general aviation most owners wait for something to break before considering fixing it because they feel preventative maintenance is too costly. If you observe operators that fly airplanes commercially and do all the maintenance their failure rates are alot less because they find the problems before they become an in flight emergency, not always but a much better record.

If memory serves, there was quite a comprehensive broken flap cable thread on this message board 6 or 7 years ago after the Australian failure. I believe that one occured on short final, a few hundred feet up, and the pilot reported he applied full power and retracted the asymetrically extended flap. It goes without saying he was probably applying full ailerons and coordinated rudder against the roll... :-)

Unfortunately, it is not possible to visually or "rag" inspect the flap cables in place, or even removed from the aircraft, because the heart strand or an internal strand may be failing, and that would not be visible externally, even with the cable removed. Also, the most common failure point is flush against a quadrant pulley, not easily inspectable.

There are FBOs who are willing to take your money for a "visual" inspection - Turbo Air in Boise Idaho did from me back in 2003 when I bought my first 1968 T337C, as part of a $7,000 annual! They called it a "visual" and "rag" inspection - you drag a rag along the cable and see if it snags anywhere, and "visually" inspect where you can't reach with the rag. This inspection was at least partly ineffectual, because it only inspected external strands, not (possibly) failing internal strands nor the heart strand.

I took a different approach with my second T337C, acquired 2 years ago with just under 3,000 hrs. TTAF: we removed the 4 flap cables which hold down the flaps and replaced them. It wasn't that awful bad a job (10 - 12 hours?), and the IA made up new cables on the spot with new terminals and cable, using a huge swedger he dragged over. I understand there's an operation in New Zealand which does same every 500-1,000 hours or so, as preventive maintenance.

Thanks for this info Paul! Much appreciated!

Ed

stainless steel or steel?
 

Does anyone know the history on when the factory went to stainless steel cables and have any of the accidents involved stainless steel cables? I understand later production aircraft were all manufactured using the stainless steal. I have heard one report that none of the flap failures involved the stainless steal equiped aircraft. This is a significant observation if true. The source did not give permission to use his name but it's a very reliable source in the 336/337 aircraft operations. OK I like cooberation. I think thats the right word.
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Weed vaporizer

If you buy new flap control cables, they are stainless steel.

We replace our cables at 3000 hrs or when we add the airplane to our fleet. I've pulled out 1800 hr cables and found broken strands and I've pulled 4000 hr cables an they were good. We replace them with stainless steel and before I install the I let them soak overnight in a Mil spec cable lube that I used on Sabreliners. It takes @ 6 or 7 hrs to change them and rigg the flaps. I also found that it is easer to remove the cable pulleys rather then removing the guard pins. They can be almost impossable to get them back in and bent over.
Hope this help
Kim

The crash of the 337 doing fire work could have been caused by the pilot making 360's at low level and flying into his own wake turbulance. this may have been what happened to an O2 a few years ago doing whale surveys off the Fla coast.
Kim