ATSB done it again?

[Lumps]

Apologies if this particular aspect of the Mojave PGW accident has been discussed before, I searched and could not find..

So what went wrong in that engine that precipitated the chain of events:

Spectral analysis of the recording indicated that the propeller RPM of the affected engine was varying from about 2,350 RPM to greater than 2,600 RPM, which exceeded the specified maximum rotational speed of 2,600 RPM.

However, the engine manufacturer advised that the surging RPM that was audible in the background to the pilot’s transmissions was ‘consistent with uneven fuel distribution to the cylinders’. The propeller manufacturer advised that it had ‘yet to find a causal factor in surging that was clearly identified as being from the propeller or governor, especially for a report of a large RPM excursion’. On that basis, the Australian Transport Safety Bureau (ATSB) concluded that it was likely that the surging was related to an uneven fuel distribution problem, rather than to a propeller/governor problem.

How on earth does uneven fuel distribution to the cylinders cause engine rpm to exceed its maximum governed speed? If that's what Lycoming told the ATSB intern that rang them then I bet they were giggling when they hung up the phone. ALL their engines have uneven fuel distribution when they leave Williamsport.

That answer, if indeed anyone actually asked Lycoming, is pure piss taking. How embarrassing. I think this shows what Lycoming thinks of the ATSBs top engine brass, after their imaginative analysis of the Whyalla accident some years ago.

[Old Akro]

I was pretty upset about this report. It is substandard, reports facts incorrectly, ignores obvious lines of enquiry and has the strench of a cover up.

The report concludes that the pilots airspeed control was inadequate, but it does this on flawed data. The ATSB used a wind vector applied to radar grounspeed to derive airspeed, but got the arithmetic wrong.

There is an extensive earlier thread. I'd encourage you to read it.

[Old Akro]

Here it is

http://www.pprune.org/pacific-genera...sb-report.html

[Lumps]

I've read it, it's what was quoted in post No1. Didn't want start another thread on the entire accident (both ended badly)

Mearly highlighting the non-fact based report writing of the atsb once again. Did Lycoming really say that? It seems too crazy to be true. If that bit is fiction then what sort of filter do we apply to all other reports.

I'd be happy with 'don't know why the engine failed' rather than just make something up. If the spectral analysisonkulator is to be believed (I dunno) then I would have thought the engine overspeed has to be governer/propeller related.

[FGD135]

Lumps,


I think you will find that, for all the CSUs fitted to piston aircraft, the CSU will allow momentary overspeeds of the prop RPM.

[Lumps]

From uneven fuel distribution?

[27/09]

I don't know about uneven fuel distribution but I do know a momentary loss of power, due for example fuel starvation due to momentary unporting of the fuel pick up, can result in an overspeed.

As the engine loses power the CSU commands the prop to full fine to maintain RPM when the power is rapidly restored the CSU cannot control the RPM fast enough to stop an overspeed.

Often on a touch and go in a CSU aircraft you will hear the RPM increase as power is applied then the RPM drops slightly. This normally happens when the pilot rams the throttle open more quickly than desirable, the CSU doesn't keep up but eventually gets the RPM under control.