ASN Wikibase Occurrence # 30518
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| Date: | Monday 7 June 1999 |
| Time: | 09:00 |
| Type: |  Hughes 369HS |
| Owner/operator: | Hoffman Helicopters Inc |
| Registration: | N4278M |
| MSN: | 23-0450S |
| Year of manufacture: | 1973 |
| Total airframe hrs: | 8168 hours |
| Engine model: | Allison 250-C20B |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | 300 miles SW of Majuro -
 Pacific Ocean
|
| Phase: | En route |
| Nature: | Survey |
| Departure airport: | Fishing Vessel, |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
About 10 minutes into a fish spotting mission from a fishing vessel, the pilot felt an intense vibration through the tail rotor pedals and helicopter control became increasingly difficult. About 250 feet above the water, the 90-degree gear box and tail rotor assembly separated. The helicopter spiraled down toward the water, spinning to the right with an estimated 55- to 60-degree nose-down attitude. The pilot reported the last moments before contacting the water were 'uncontrollable.' The helicopter was recovered, except for the tail rotor system rotating components and gearbox. The operator reported that he had removed the tail rotor abrasion strips from the blades during an annual inspection about 73 hours before the accident. He reported that he applied 'direct and intense heat' to the blades to remove the strips. According to the manufacturer, the abrasion strips can be removed; however, it must be done by an approved blade overhaul facility and cannot be accomplished in the field. The manufacturer stated that the use of heat is unauthorized and likely induced a bond separation within the tip cap area. A review of the McDonnell Douglas maintenance manual revealed that tail rotor blade repairs are not specifically addressed. A McDonnell Douglas representative reported that if a repair is not addressed in the manual, it is not authorized. He stated that certified blade repair stations are authorized expanded repairs. The pilot/mechanic reported that he was aware that the operator had removed the tail rotor abrasion strips and had observed a small gap between one of the tail rotor blade tip caps and the blade during a routine inspection before the accident. He contacted the operator and requested a new blade. He then applied clear epoxy resin at the joining surfaces then test-flew the helicopter and noticed 'no change in the flight characteristics of the aircraft.' He stated that he felt the 'blade [was] airworthy and was as originally constructed.' McDonnell Douglas Service Bulletin HN-195 directs mechanics to visually inspect the tip cap-to-blade bonding for failure and states that 'if any evidence of debonding is noted, replace blade.'
Probable Cause: The removal of the tail rotor blade abrasion strips by the use of an unapproved method by the maintenance personnel which resulted in the imbalance of the tail rotor blade assembly and subsequent separation of the 90-degree gear box; the pilot/mechanic's unapproved repair to the tail rotor blade tip caps; and, his continued operation of the helicopter with known deficiencies.
Sources:
NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20001212X19048&key=1
1. https://flightaware.com/resources/registration/N4278M
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 27-Sep-2008 01:00 | ASN archive | Added |
| 22-Feb-2015 23:52 | Dr. John Smith | Updated [Operator, Total fatalities, Total occupants, Other fatalities, Location, Country, Phase, Nature, Source, Damage, Narrative] |
| 14-Dec-2017 08:29 | ASN Update Bot | Updated [Time, Cn, Operator, Total occupants, Departure airport, Source, Narrative] |
| 06-Jun-2022 04:30 | Ron Averes | Updated [Aircraft type, Cn, Operator, Location, Country, Source, Narrative] |
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