Comments are coming due on a draft Federal Aviation Administration (FAA) advisory circular (AC) dealing with engine safety analysis (i.e., risk factors). AC 33.75-1 was published July 21 in the Federal Register (FR Doc 04-16522) with an Oct. 31 deadline for comments.

The draft AC is intended to replace the previous guidance, AC 33-2B. The new document seems to embody a comprehensive approach overall, albeit one that may be making too fine a distinction between "aircraft level" failure and "engine level" failure. Although maintenance errors as contributing to engine safety are mentioned in paragraph 16 of the draft AC, which urges engineers to consider ease of maintainability in their engine designs, the notion of "induced" errors might warrant more attention.

The aspect of induced errors as contributing to engine failure might appropriately be addressed in paragraph 6. This paragraph says that it must be shown by analysis that any failure or combination of failures will not cause the engine to (a) catch fire, (b) burst (e.g., release hazardous fragments through the engine case, (c) exceed ultimate design loads, or (d) lose the capability of being shut down.

To these, one might add a subparagraph (e), perhaps titled "fail to function as a consequence of induced failures." We can conjure a list, some of which can be parsed as "engine level" effects with others as "aircraft level" failures. That having been said, here's a list of such induced failures:

• Air Transat's A330 maintenance-induced loss of all fuel.
• The recent airworthiness directive about cross-wired fire extinguishers/buttons on the BAe 146 ("Murphy's Law").
• Failed thrust reverser interlocks (to avoid reverse thrust in flight)
• Water ingestion from nose wheels on wet runways (a bane of rear engine twinjets).
• Ice shed from the wings and ingested into the engines on takeoff (which dumped an SAS MD-80 into a field).
• Systems related fuel starvation (the Gimli Glider).
• TOGA (take off go around) button/switch confusion.
• Software commonality and FADEC (full authority digital electronic control) interfaces.
• Cowling-shedding incidents, such as those affecting the A319/A320/A321 family.
• Electromagnetic interference (EMI) effects on engine-mounted electronics.
• Bird strikes, which do not appear to be mentioned at all in the draft AC, but which have caused a fair number of engines to ingest "bird slurry" of late. In a 2002 presentation, Richard Dolbeer, chairman of the National Birdstrike Committee, suggested that engine designs may have to be beefed up to safely ingest an 8-lb. bird. That's a dramatic increase over the present 4-lb. standard, but with more large birds flying nowadays, the time has come for a tougher bird ingestion standard, Dolbeer suggested. Yet the words "bird" or "bird strike" nowhere appear in this draft AC.

This much can be said: induced failures must be one of the big players in engine safety and getting bigger as maintenance error and outsourcing ties in with lowering experience levels. Engine maintenance error in the Air Sunshine crash is a case in point.