Hughes OH-6A accident near Aguadilla, Puerto Rico, July 29, 1999
On July 29, 1999 at about 1:15 pm local time, a Hughes OH-6A (helicopter), registered N66377, was substantially damaged in an accident near Aguadilla, Puerto Rico (Unknown airport). It was a public-use flight under general aviation rules (Part 91). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
An unidentified foreign object passing through the oil cooler blower assembly resulting in fracture and seizure of the oil cooler blower, and slowing of the main transmission and main rotor, which resulted in the pilot being unable to arrest the descent during an autorotative landing.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 29, 1999 · about 1:15 pm local time
- Place
- Aguadilla, Puerto Rico · Unknown · map
- Type
- Accident · collision on the ground
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Hughes OH-6A · all OH-6As on the register
- Registration
- N66377 · no longer on the register · serial 67-16571
- Damage
- Substantial damage
- Flight
- Public-use flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
While in cruise flight at 800 feet, the pilot heard a metal grinding noise followed by the engine failure warning. The pilot entered autorotation and during landing flare he was unable to arrest the descent, resulting in a hard landing and damage to the helicopter. Postcrash examination of the engine and engine systems showed no anomalies. Examination of the main transmission showed no damage which cause seizing of the transmission. Examination of the oil cooler blower assembly showed one impeller blade was fractured due to overload which opened a two inch gap in the impeller. The blower stopped spinning and sheared away from the adapter. The impeller shroud had abrasion damage and some minor areas of debris buildup. The oil cooler is driven by the main transmission.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: commercial pilot
- Ratings: single-engine land; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 751 hours in all; 479 in this make and model; 572 as pilot in command
- Last flight review: January 1, 1999
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 2,567 hours
- Last inspection: approved inspection programme, July 15, 1999; 10 hours since
- Maximum gross weight: 2,550 lb
- Seats: 4
- Landing gear: fixed
- Engine: Allison 250-C20B (turboshaft); 0 hours total
The flight
- Departed from: BQN
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 100° at 10 knots
- Visibility: 14 statute miles
- Sky: clear
- Temperature: 82°F (28°C), dew point 73°F (23°C)
- Altimeter: 30.04 inHg
- Observation at 12:50 pm from BQN, 8 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.