Service Difficulty Advisory
31 January 2000
Mcdonnell Douglas (Hughes)
369 Series Flight in Falling Snow - Optional Engine Air Inlet Deflector
An engine failure in an MD 369D caused a forced landing and roll-over with serious injuries. The engine auto re-ignition system was ON and the engine anti-ice OFF. The environmental conditions were light snow, 5000 foot elevation, light winds and minus 3° C. The investigation concluded the helicopter experienced a sudden engine flameout during climb-out, likely as the result of the dislodging of a snow deposit in the air inlet plenum. A contributing factor was that the optional engine air intake deflector kit had not been installed on this helicopter.
In a second accident an MD 369HE suffered an engine failure during takeoff from a confined location and conducted a forced landing with several serious injuries. The auto re-ignition system was OFF and the engine anti-ice ON. The environmental conditions were light snow, 800 foot elevation, 22 knot winds and minus 12° C. Although the investigation is clear that the auto re-ignition system could have prevented this crash, it also offered the following anecdotal evidence.
Interviews conducted with eight representatives of five Canadian operators of Hughes 369 helicopters universally supported the use of the optional air inlet deflector kits. One operator said that they "would not operate in falling snow without them". Another operator reflected that they had numerous flameouts while operating in snow and after installing deflector kits, "the problem vanished overnight".
The MD 369 helicopter is certified for flight in falling snow only if the Engine Failure Warning and the Engine Automatic Re-ignition systems are installed and operational. Use of the Engine Anti-Ice system is required when the OAT is less than 5° C and when visible moisture is present. An optional kit for this helicopter is the Engine Air Inlet Deflector (Part No. 369D292044-501 or 369D292045) which is recommended for use in dust/sand and snow environments. The Allison 250 series engine is prone to flameouts in snow conditions as identified in an Allison Commercial Service Letter CSR-106 and CSL-1092 Rev. 2, 30 September 1982. Snow or ice which builds up in the inlet plenum area can break free in "slugs" and cause flameout.
The Transportation Safety Board of Canada has suggested that Transport Canada review the certification of this helicopter for flight in falling snow and perhaps mandate the use of deflector kits. Transport Canada has forwarded this recommendation to the FAA. Pending resolution of this issue by TC and the FAA, MD 369 helicopter operators in Canada are strongly urged to use the Engine Air Inlet Deflector kit when flight into falling snow can be expected.
For more information, contact a Transport Canada Centre or Mr. Alan Stewart, Continuing Airworthiness, Ottawa, telephone (613) 941-8385, facsimile (613) 996-9178, or e-mail firstname.lastname@example.org.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness
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