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Oh No, not the LOP/ROP debate again. Following are excerpts from two recent posts on the subject from the Mooney Mailing List, passed along without comment on the ROP/LOP issues:
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Trevor Bennett Wrote:
Was wondering how many pilots saw R. Collin's 'On Top' column in May, Flying mag, re the accident report, "Bad Dream," on the Australian Piper Navajo Chieftain, (Turbo) that lost both engines, at night, over water & all aboard perished??
Collins says the ATSB report (138 pages) is the most complete accident report on a mechanically-related GA piston airplane accident that he has ever seen.
The left engine apparently failed first, from a fatigue crack in the crankshaft. (I'll try to keep this short.) The report said "the combined effect of high combustion gas pressures that developed as a result of deposit-induced pre-ignition and lowered bearing retention forces, due to an 'anti-galling' lubricating compound used during engine assembly by the manufacturer, led to the breakdown." The engine had approximately 262.1 hours on it since factory overhaul.
Then, the right engine failed, likely because of detonation when power was increased to maintain altitude to compensate for the failed left engine. The "detonation rapidly increased engine temps & a hole melted in the #6 piston, causing loss of engine power & erratic operations." In moments, "the hot combustion gasses blowing past the burned piston destroyed the right engine."
The article points out that high engine temps can be reduced by enriching the mixture, which we all know. But the ATSB made much of the engine leaning practices used by the operator. It states that while "they were within the engine operating limits set by the engine manufacturer, the ATSB said that they (the leaning practices) increased the likelihood of lead oxybromide deposit-induced pre-ignition." The operator followed the practice of leaning while at climb power and leaning to "best economy" in cruise.
It was suggested that some pilots operated the engines lean of peak EGT. The ATSB found that these practices could result in the formation of deposits on cylinder and piston surfaces that could cause pre-ignition.
Finally, the report included pictures of cylinders and pistons that had been run (either) leaner or richer. The richer ones--operated full rich for climb, & at "best power mixture" for cruise--showed much less deposit. Collins sums it up by saying, "
I know there are pilots who love to brag about how much fuel they save by running engines lean, but this (complete) report sure casts a technical shadow on that practice." He concludes by saying, "if you fly a highly-stressed piston engine, the next time you start 'back' with the mixture, think about a 22-year-old Captain with seven passengers on board, faced with a night-ditching with no landing lights available (because they were attached to the gear, which had to be up for a water crash-landing) after both engines quit, possibly because of the way the engines had been operated."
The accident occurred in the Spencer Gulf, May 31, 2000. Full report is at: http://www.atsb.gov.au/aviation/occurs/occurs_detail.cfm?ID=317
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For an opposing point of view:
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Roger Allison-Jones:
Before anyone starts getting too excited, there is a MASSIVE controversy raging, to say nothing of battered egos, at the moment, about this report. "FLYING" magazine heaped compliments onto the report, but Deakin, from Avweb, has labelled the ATSB report as "poppycock" and "old wives tales". Please read his article at http://www.avweb.com/articles/pelperch/pelp0057.html
The ATSB has responded, in high dudgeon, with this article:- http://www.atsb.gov.au/atsb/media/whyalla_report.cfm The cornerstone of the argument would seem to be whether "Lead Oxybromide" is in fact a factor or have ATSB merely used it to justify the conclusions that they WANTED to draw.
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One incontrovertible thing that we can all learn from this accident report is the wisdom of having landing lights on the landing gear. Even if we don't ever plan to put ourselves in a position of having to face the possibility of ditching at night, just a "normal" failure-to-extend emergency with the landing gear at night could get a lot more stressful if you loose the landing lights in addition to the landing gear.
Hamid
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