Mbb BK-117-B2 accident near Fresno, Texas, July 17, 1999
On July 17, 1999 at about 5:31 pm local time, a Mbb BK-117-B2 (helicopter), registered N110HH, was destroyed in an accident near Fresno, Texas (Lifeflight Refuel airport). It was a positioning flight under general aviation rules (Part 91). 3 people were killed. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
the loss of control during approach due to the corrosion of the T-T strap which resulted in fatigue cracking and subsequent separation of the strap and main rotor blade from the helicopter.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 17, 1999 · about 5:31 pm local time
- Place
- Fresno, Texas · Lifeflight Refuel · map
- Type
- Accident
- Injuries
- 3 people were killed.
- Weather
- visual conditions (good weather)
- Aircraft
- Mbb BK-117-B2
- Registration
- N110HH · registry record · serial 7122
- Damage
- Destroyed
- Flight
- Positioning flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The helicopter was making a VFR approach to a fueling site when witnesses observed components of the main rotor system separate from the helicopter. Subsequently, the helicopter entered an uncontrollable descent and impacted the ground. Examination of the helicopter revealed that one of the four main rotor blades separated due to the failure of the tension-torsion strap (T-T strap), which secured the blade to the main rotor head. Examination of the failed T-T strap revealed that the polyurethane protective coating had debonded from a portion of the strap allowing corrosive agents, including carbon, sulphur, and chlorine into the strap. The strap separated as a result of fatigue cracking of the wires making up the strap. The fatigue cracking emanated from corrosion pits and deposits that were introduced to the strap when the polyurethane protective coating debonded. The T-T strap had accumulated a total of 7,815.3 flight hours and 35,971 flights at the time that it failed. It had been in service since the helicopter was manufactured in 1987. Following the accident, a life limit of 120 months or 25,000 flights (whichever comes first) was established for the T-T straps.
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: airline transport pilot, commercial pilot
- Ratings: multi-engine land; single-engine land; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 9,233 hours in all; 33 in the last 90 days; 22 in the last 30 days; 9,233 as pilot in command
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: rgt
The aircraft
- Airframe total time: 7,815 hours
- Last inspection: approved inspection programme, July 7, 1999; 25 hours since
- Maximum gross weight: 7,055 lb
- Seats: 8
- Landing gear: fixed
- Engine: Honeywell LTS101-750B-1 (turboshaft); 0 hours total
The flight
- Departed from: 20TA Houston TX at 5:26 pm
- Destination: TE11 Fresno TX
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 160° at 7 knots
- Visibility: 10 statute miles
- Sky: broken clouds at 7,000 ft; scat at 3,000 ft
- Temperature: 88°F (31°C), dew point 75°F (24°C)
- Altimeter: 30.00 inHg
- Observation at 4:53 pm from HOU, 10 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 3 |
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.
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number FTW99FA192.