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Oops, darn it...

Just heard a Mayday call on 122.9. I was about 24 miles N of Sun Valley Idaho amongst peaks so mtns might have played a factor in the faint reception.

Pilot said he was over Jack’s Peak (?) then his signal cut out.

I reported info to Sun Valley tower. They said they were “working their resources” to try to find others who might have heard the transmission.

Sure got my attention. Raises the hair on my neck.

If anyone gets more info please post or PM me.
 
tedwaltman1 said:
Just heard a Mayday call on 122.9. I was about 24 miles N of Sun Valley Idaho amongst peaks so mtns might have played a factor in the faint reception.
Pilot said he was over Jack’s Peak (?) then his signal cut out.
...
Click to expand...
Most likely calling over Jackson Peak (there's a fire lookout there), a few miles southwest of Warm Springs airstrip. Hope he made it.
 
I heard Center asking another pilot to call w the additional info that pilot had. Kind of sounded like the other pilot was a lot closer and/or saw the accident.
 
Heard a red and white cub went down over in the Pt McKenzie area last night about 7:30, two souls on board were transported to a Anch hospital. I don't know the severity but prayers non the less they are OK.
 
DHC-3 Fatalities Off Whidbey

A DHC-3 crashed off of Whidbey Island, WA last Sunday. Eye witness reported that “the aircraft dropped suddenly at a fair amount of speed and hit the water.” Pilot plus 9 PAX onboard with no survivors. Very little debris recovered so far and one body - probably in fairly deep water. I’m told there was a safety directive issued last year on this aircraft type but don’t know if it had any bearing on this kind of accident.

I’m interested in thoughts from those with experience in the DHC-3.

Thoughts and prayers for the lives lost and their loved ones!

https://www.kitsapsun.com/story/new...crash-included-activist-winemaker/8000357001/

https://www.asias.faa.gov/apex/f?p=...MAKE_NAME,P96_FATAL_FLG:06-SEP-22,DEHAVILLAND



 
Video put up quick. Sounds like it will be removed shortly. Quite sad. My question to those that fly these. When a turbine is hung on a airframe designed for radial engines and slower speeds, what does that do to fatigue?




 
I hope the airplane is recovered for the families and the investigation. Three possibly related events in the previous 25 years may warrant a closer look but it isn’t a smoking gun.
 
scout88305 said:
Video put up quick. Sounds like it will be removed shortly. Quite sad. My question to those that fly these. When a turbine is hung on a airframe designed for radial engines and slower speeds, what does that do to fatigue?




Click to expand...
Thank you for this, he makes a lot of sense and seems to have a handle on a likely probable cause. I have heard when an airplane is converted from a recip to a turbine the natural resonant frequency does change. This means that a part which works well for decades suddenly becomes dangerous. A few years ago the FAA mandated changing from a single to a dual actuation in certain trim systems. Perhaps we'll never know the true failure of this airplane? It is possible that a failure of some portion of the pitch trim could have allowed the trim tab to flutter. I can tell you from personal experience that can happen instantaneously without warning. When a trim tab flutters, everything it is attached to also moves following the tab's action. A failed tab could cause the entire tail to separate from the airplane. In my case I was able to keep the airplane under control to the landing, with difficulty.

I do know if I had a turbine Otter, that tail would now be undergoing an extensive inspection. Doesn't Dave Calkins fly one of these?
 
scout88305 said:
My question to those that fly these. When a turbine is hung on a airframe designed for radial engines and slower speeds, what does that do to fatigue?
Click to expand...

I do not fly those, but I do have a pair of S2R's that started as R1340's and now sport the same engine and prop combination as the plane in this accident as well as the one that went down in Yakutat.

The engine (M601E-11A) and prop (which was a 108" Avia not a Hartzel... sorry Dan) are a great combination, but your question has a lot of merit. S2R's have a spar life, and various spar related AD's, but to your point, that spar life has a series of formulae and that life changes from a 'life long' recip, to a 'turbine converted from recip', and is also different than a 'born' turbine. I have no idea what that means for the tail, and personally would lean towards a corrosion or fatigue failure, but like Pete, if I owned a turbine single otter, I'd be knee deep in the tail. I feel almost fortunate that my converted airplanes both sport fabric tails that require almost non stop attention.... Ignorance is only bliss until something bad happens of it.

Take care, Rob
 
If potential flutter in DHC-2 or -3's is a known issue, then why isn't it a constant monitoring task? Maybe it is - don't know. Maybe the turbines blow more airflow over the tail or increased airspeed make it more critical? Airspeed indication versus true airspeed may not be the same especially if demonstrated Vne is approached.

Gary
 
BC12D-4-85 said:
If potential flutter in DHC-2 or -3's is a known issue, then why isn't it a constant monitoring task? Maybe it is - don't know. Maybe the turbines blow more airflow over the tail or increased airspeed make it more critical? Airspeed indication versus true airspeed may not be the same especially if demonstrated Vne is approached.

Gary
Click to expand...
Potential flutter of the type we are talking about is possible on any airplane which has a trim tab on the elevator(s). For any number of reasons. The change from recip to turbine isn't necessarily the speed of the airplane, more likely the speed of rotation of the engine. The recip in this case is normally rotating in the 2000 rpm range with a singular periodic piston impulse. The turbine rotates in the 10,000 +/- range with a steady high frequency "buzz". These engine produced vibrations travel throughout the airframe, coming out at the wing tips and tail. Those components which were designed to function without issue with the recip, sometimes can not safely function without failure at the higher frequency. This is partially why some components have a lifetime time or cycle limitation for inspection or removal. The tail being at the opposite end of the fuselage from the engine is the most susceptible to these forces.
 
With the exception of the last 10 years or so of production, all Ag Cat’s started life as a radial and were converted to turbine. I’ve worked around a few that are 15k+ hrs of turbine time and don’t show any abnormal wear from the turbine, mine has 3k hrs with a turbine after 8k hrs of a radial and is fine. My mechanic says the only issue he’s seen turbine related is a twisted frame from over-torquing on takeoff. However, an Ag Cat is quite possibly the most overbuilt and rugged ag plane built, they’re incredibly easy to inspect and get in front of repairs before something breaks from fatigue. I’ve never been around an Otter or Beaver during annual so I don’t know how hard a turbine is on the airframe, but a Thrush is the only other ag plane that comes close to the ruggedness of a Cat.
 
Other than both the Trush and the Cat having tubular fuselages vs the Beaver and Otter's sheet aluminum they all have trim tabs on the elevators. One little failure which allows the tab to free float can result in (possibly instantaneous) disaster.
 
Cruise RPM for PT6 Otter is 17-1900 and Garrett is high 1500's. Walter is similar to the PT6. Turbines will turn in the 30-40.000's. IAS is limited to speeds similar to piston models. There is a lot of maintenance focus on the flight control systems and wing strut assemblies.
 
I wonder if turbine powered DHC-3's deflect or at least deploy the elevator trim more or more frequently during normal ops?

Gary
 
Otter pitch trim is a trimmable stabilizer hinged at the front with a jack screw in the back. A servo tab is on the right elevator and and extra-large chord trim tab on the left elevator is linked to the flaps, which adds nose down trim when flaps are deployed. This system is not original, but was installed via a service bulletin/kit not long after they were built. There is currently an AD requiring 100hr inspections of the tab slop, due to previous issues such as noted above. The flap trim tab especially has a lot of rod ends and connections that make up the linkage. Part of the pt-6 conversion is adding a redundant second pushrod on the servo tab on the right side, but it’s not required on the Garret- always made me think it’d be a good idea...
 
It’s remarkable that the failure of such a relatively small piece of metal can exert such enormous force on the controls that very strong men and women can’t overcome its effect. What makes this story truly tragic is that no one has bothered to come up with a safe, inexpensive, and reliable permanent fix after so many years witnessing such heartbreaking events.
GA, Dehavilland, Harbor Air, Kenmore, etc. all risk losing everything if one of theirs breaks. Crossing your fingers or knock wood doesn’t seem to cut it.
 
This type of control problem isn’t all that uncommon, the Twin Bee has a elevator tab that will crash the plane if the control rod comes off.
 
This last bit of discussion about the catastrophic loss of a control surface on the turbine float plane made me try to think about what I might do if some similar disaster occurred on my PA-11. Let's say an aileron/rudder/elevator cable breaks or comes disconnected, or a pulley/wheel falls loose, or a pivot pin falls out, or etc. Hmmm. My poor little brain was immediately tied in knots. With the elevators I did have some side thoughts to engage as regards the trim cables; but all in all, I could not get far in trying to think of alternatives for quickly developing alternative methods of control sufficient to execute a survivable crash/landing. I think I remember a story of someone having some failure of control for elevators but managed to survive with a mix of trim and throttle control. A full on discussion of such events here would occupy the next two years! But it occurs to me to wonder if anyone has ever done a full on study of these possibilities for a simple cub-styled plane and written a book about it. Anyone heard of such?
 
Paul Heinrich said:
It’s remarkable that the failure of such a relatively small piece of metal can exert such enormous force on the controls that very strong men and women can’t overcome its effect.
Click to expand...

algonquin said:
This type of control problem isn’t all that uncommon, the Twin Bee has a elevator tab that COULD crash the plane if the control rod comes off.
Click to expand...
I changed your will to could. It has never reached my ears that a Twin Bee did crash due to this issue. Most, if not all of them which are gone are due to pilot errors or mishandling an engine failure (again, pilot error).

It did almost happen when the push rod (Piper PA-23 part) broke. It took two of us holding the controls with all our might in order to attempt to reduce the flutter. It's hard to say at this point in time whether we had much effect. The flutter did not stop until the wheels rolled on the ground. The only thing I can be certain of is, slowing the airplane had the most effect at reducing the flutter forces.

This airplane has a long balance arm with a lead weight on it extending forward of the elevator control horn. Due to a ground flutter analysis test the weight of the lead was increased. The arm was then tested for the increased G loads and found to meet the FAA requirements of +/- 14 g in one direction and +/- 28 g in the other. ( I forget the actual G loads, But they are huge). When we got the airplane back to the hangar we found this arm twisted like a pretzel and rubbing on one of the elevator cables. It came that close to breaking the elevator cable.

Paul, an earlier incident with this same trim tab happened when it set up a high frequency "buzz" While doing a high speed dive test (not yet at the objective speed). This "buzz" transmitted into the push rod which was controlling it. The oscillations of the push rod exceeded the bending strength of the rod while under compression causing it to buckle. During this process the elevator was destroyed. This particular issue was solved by placing the bellcrank on the opposite side of the tab and changing the winding of the trim cable so that the rod "pulled" in this trim condition rather than "pushing".

I don't doubt for a minute that one of the components which ak49flyer described could have failed causing this Otter to crash. Most pilots and mechanics do not realize how critical these trim tab components are. Take this as a heads up from someone who has been there more than once ..... and survived.

I know of one other example in which this same thing happened (tab push rod separated) on short final to landing with a Fairchild FH-227 at PWM. The pilots had their hands full, but also were successful in landing.
 
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