Alaska Air Crash Investigation.

[planedriver]

Reminder for anyone interested. It's on Ch 1 Sydney now.

 

I missed it it last week..

 

 

[poteroo]

Accident #1

 

Deliberate low flying in Cessna 206 for mates' party - struck tree - crashed inverted - fatal.

 

Accident #2

 

Maintenance test flight in Cessna 207 - pilot overcome by CO in cockpit from non-standard heater muffler installation - fatal

 

Again, a good program showing the US NTSB working through GA accidents in Alaska - although both of these accidents could have been anywhere in the world.

 

 

[dsam]

Regarding Accident #2 - I thought CO warning stickers were mandatory?

 

Knowing the cold weather in Alaska, I understand why they would like to boost-up the heating system, but non-standard modifications are just asking for trouble. Since they still went ahead and did that modification, why wouldn't they have done ground tests after such a significant change!! Both tragic crashes were avoidable - sadly so many are...

 

 

[Smokey]

I missed it it last week..

For those that missed either, episodes 1 & 2 are available on tenplay.

 

Alaska Aircrash Investigations

 

Mark

 

 

[Gravity]

Thanks for the link

 

 

[dsam]

Ok, the latest episode entertained the possibility of fuel cavitation & subsequent engine faltering following a sudden 45 degree climb and levelling out manoeuvre (occurring in the float chamber, I’m assuming?)

 

I can understand such cavitation from a vibration at just the right frequency, but I’m not sure I understand how low or zero g leads to such cavitation.

 

Can anyone clarify how that happens?

 

 

[Gravity]

Ok, the latest episode entertained the possibility of fuel cavitation & subsequent engine faltering following a sudden 45 degree climb and levelling out manoeuvre (occurring in the float chamber, I’m assuming?)I can understand such cavitation from a vibration at just the right frequency, but I’m not sure I understand how low or zero g leads to such cavitation.

Can anyone clarify how that happens?

Probably pushed it over rather abruptly causing neg G's, been done before many a time.

 

 

[dsam]

....yes, but why would cavitation occur from that?

 

 

[Gravity]

....yes, but why would cavitation occur from that?

Cavitation is just the word they used, the result was an interruption of the correct air fuel ratio.

 

 

[poteroo]

May not have been due to any carby effect of the negative G's in the reported pushover. May have been due to 'unporting' in the fuel tank outlets - especially if the tanks were low on contents. However, the wreckage carried a strong fire, so there must have been some quantity of fuel remaining.

 

I've flown a large number of C180s and, because I always select BOTH ON with fuel - very few of them drain fuel out evenly. Try as one may at holding perfect balance, it seems that one tank will drain ahead of the other - L usually. Once the 'usable' fuel is drained down to the 'unusable' level, the fuel port is close to exposed and air could get into the fuel lines. Unporting due to negative G might create this situation - even with usable fuel remaining in the tank.

 

With the fuel selector set on L or R tank, the unporting, (of the tank in use), could happen while the aircraft still had adequate flight fuel on board. In which case, the aircraft engine could suffer temporary/intermittent fuel flow, which could be critical if flying low, as this aircraft was reported. I'd be very interested if the NTSB had published where the fuel tank selector was set.

 

As a warning to Aussie pilots, if you have been taught to always select C100 series aircraft fuel to L or R, instead of BOTH, then go and read the POH. You'll find that it says - fly on BOTH unless you have a damned good reason not to. I have seen so many 'Pilot Notes' which say to fly on one or the other and time your use. Yes, time your use, but don't fiddle with the fuel tank selector!!

 

If your Cessna 100 series tanks don't drain evenly: (1) learn to fly in balance (2) adjust the tank vents

 

Explanation: The fuel tank selector handle is locked with a pin/screw arrangement onto the vertical shaft, which gradually bells out, and you can feel the sloppiness in the handle. The ports in the selector body are only open for a few degrees, and for them to be fully open - the selector must click into the relevant detent. No click = not full fuel flow. Failing to get the selector to click into the detent can, and has, caused fuel flow interruption and a forced landing. Therefore - don't rely on your visual check that the selector is pointing towards the desired position - turn until the detent is felt, regardless of the selector indicator being as much as 10 degrees 'away' Fuel selectors come as a complete unit and cost a 4 figure number - as you'd expect with Certified aircraft.

 

 

[dsam]

...May have been due to 'unporting' in the fuel tank outlets - especially if the tanks were low on contents. However, the wreckage carried a strong fire, so there must have been some quantity of fuel remaining....

Yes, that explanation makes more sense than “cavitation” (at least in the sense that I understand the word).

Having a LAME as an eyewitness should have given the investigators much more confidence in that particular account of the accident. Given how ubiquitous aviation is in the Alaskan community, the investigators there must have more useful accounts from eyewitnesses, than investigators in more urbanised settings.

 

As for L&R tanks draining unevenly, my Eurofox tanks have clear plastic tubes as an extra visual indication of fuel remaining in each. Over a 3+ hour flight with both fuel valves open, invariably one tank drains somewhat more than the other - and not always the same side. I’m mostly on autopilot on such long legs, so the wings are consistently kept level. I’m not especially bothered, as I can easily see and rectify this in flight, but it is a quirk that puzzles me.

 

 

[poteroo]

As for L&R tanks draining unevenly, my Eurofox tanks have clear plastic tubes as an extra visual indication of fuel remaining in each. Over a 3+ hour flight with both fuel valves open, invariably one tank drains somewhat more than the other - and not always the same side. I’m mostly on autopilot on such long legs, so the wings are consistently kept level. I’m not especially bothered, as I can easily see and rectify this in flight, but it is a quirk that puzzles me

Is the ball precisely centered while on a/p? Your a/p may well fly you on a straight track, but it could do this with crossed controls.

 

 

[facthunter]

The slightest difference in vent pressure would bias the system. School aircraft like the gazelle can show marked difference in fuel level. I put it down to flying unbalanced. Nev.

 

 

[Gravity]

May not have been due to any carby effect of the negative G's in the reported pushover. May have been due to 'unporting' in the fuel tank outlets - especially if the tanks were low on contents. However, the wreckage carried a strong fire, so there must have been some quantity of fuel remaining.I've flown a large number of C180s and, because I always select BOTH ON with fuel - very few of them drain fuel out evenly. Try as one may at holding perfect balance, it seems that one tank will drain ahead of the other - L usually. Once the 'usable' fuel is drained down to the 'unusable' level, the fuel port is close to exposed and air could get into the fuel lines. Unporting due to negative G might create this situation - even with usable fuel remaining in the tank.

 

With the fuel selector set on L or R tank, the unporting, (of the tank in use), could happen while the aircraft still had adequate flight fuel on board. In which case, the aircraft engine could suffer temporary/intermittent fuel flow, which could be critical if flying low, as this aircraft was reported. I'd be very interested if the NTSB had published where the fuel tank selector was set.

 

As a warning to Aussie pilots, if you have been taught to always select C100 series aircraft fuel to L or R, instead of BOTH, then go and read the POH. You'll find that it says - fly on BOTH unless you have a damned good reason not to. I have seen so many 'Pilot Notes' which say to fly on one or the other and time your use. Yes, time your use, but don't fiddle with the fuel tank selector!!

 

If your Cessna 100 series tanks don't drain evenly: (1) learn to fly in balance (2) adjust the tank vents

 

Explanation: The fuel tank selector handle is locked with a pin/screw arrangement onto the vertical shaft, which gradually bells out, and you can feel the sloppiness in the handle. The ports in the selector body are only open for a few degrees, and for them to be fully open - the selector must click into the relevant detent. No click = not full fuel flow. Failing to get the selector to click into the detent can, and has, caused fuel flow interruption and a forced landing. Therefore - don't rely on your visual check that the selector is pointing towards the desired position - turn until the detent is felt, regardless of the selector indicator being as much as 10 degrees 'away' Fuel selectors come as a complete unit and cost a 4 figure number - as you'd expect with Certified aircraft.

Whilst unporting was possible I doubt it, there would be enough fuel from the pick up point of the tank/s to the carby plus the carby bowl contents to run the engine during any short term neg pushover.

 

Most aircraft with twin tanks overhead such as Cessna, Belanca etc rarely drain evenly that's one of the reasons why they are selectable to balance as required

 

 

[Happyflyer]

Whilst unporting was possible I doubt it, there would be enough fuel from the pick up point of the tank/s to the carby plus the carby bowl contents to run the engine during any short term neg pushover. Most aircraft with twin tanks overhead such as Cessna, Belanca etc rarely drain evenly that's one of the reasons why they are selectable to balance as required

I don’t think the Bellanca 8KCAB had selectable tanks. Certainly the modern versions, the American Champion Super Decathlon and Scouts manage twin overhead tanks without selectable tanks, just a shutoff valve.

 

 

[Gravity]

I don’t think the Bellanca 8KCAB had selectable tanks. Certainly the modern versions, the American Champion Super Decathlon and Scouts manage twin overhead tanks without selectable tanks, just a shutoff valve.

I guess my comments could be read that way, it was more ref to the twin overhead tanks with the Cessna type being selectable.

 

 

[dsam]

 

The slightest difference in vent pressure would bias the system. School aircraft like the gazelle can show marked difference in fuel level. I put it down to flying unbalanced. Nev.

This photo is typical of a cruise on autopilot - ball central, wings level - note wind aloft. I’m suspecting slight vent pressure variations. Tank usage differentials are usually less than 5 litres over 3 hours.

 

 

[dsam]

Latest episode: DHC-3 on floats, Impact with terrain shortly after takeoff, overweight, pre-dawn.

 

Question: Can anyone having familiarity with floats confirm the likelihood of float-underside buckling caused by a “touch & go” takeoff as described by the witness (ie. possibly a premature rotation due to being above MTOW).

 

I would have thought such float buckling would be as a result of normal shoreline mooring damage on submerged rocks, driftwood etc.?

 

 

[frank marriott]

Tank usage differentials are usually less than 5 litres over 3 hours

<5ltrs I wouldn’t even consider.

Remember if a large out of balance does occur then just feed in half a ball of skid and watch the transfer back.