Mbb BK 117 B-1 accident near Sonestown, Pennsylvania, January 27, 1991
On January 27, 1991, a Mbb BK 117 B-1 (helicopter), registered N891GM, was destroyed in an accident near Sonestown, Pennsylvania. It was an other work-use flight under general aviation rules (Part 91). 4 people were killed. The weather was instrument conditions (cloud, fog or low visibility).
The NTSB's probable cause their words, unchanged
THE PILOT'S INADEQUATE PREFLIGHT PLANNING TO ASSURE THAT THE INTENDED COURSE AND ALTITUDE PROVIDED ADEQUATE TERRAIN CLEARANCE. CONTRIBUTING FACTOR(S) WAS: THE DARK NIGHT, SNOW AND MOUNTAINOUS TERRAIN.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- January 27, 1991
- Place
- Sonestown, Pennsylvania
- Type
- Accident
- Injuries
- 4 people were killed.
- Weather
- instrument conditions (cloud, fog or low visibility)
- Aircraft
- Mbb BK 117 B-1
- Registration
- N891GM · no longer on the register · serial 7153
- Damage
- Destroyed
- Flight
- Other work-use flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
THE MEDIVAC HELICOPTER WAS RETURNING TO SAYRE AFTER TRANSPORTING A PATIENT TO DANVILLE. RECORDED RADAR DATA AND DATA OBTAINED FROM THE HELICOPTER'S LORAN-C MEMORY INDICATES THAT THE FLIGHT WAS FOLLOWING A DIRECT COURSE FROM THE GEISINGER MEDICAL CENTER AT DANVILLE TO THE ROBERT PACKER HOSPITAL AT SAYRE. THE ACFT'S HSI WAS SET TO DISPLAY LORAN COURSE INFORMATION. THE CLOSEST POINT OF THE COURSE TO THE CREST OF NORTH MOUNTAIN WAS APRX 3/4 MILE TO THE WEST. THE PILOT HAD ADVISED WILLIAMSPORT ATCT TRANSITTING THEIR CONTROL ZONE AT 2,500 FT. IMPACT OCCURRED AT 2,440 FT MSL. THE CREST OF THE RIDGE IS 2,520 FT MSL WITH 40-FT HIGH TREES. A WITNESS WHO LIVES IN A CABIN ON THE MOUNTAIN 200 YARDS FROM THE ACCIDENT SITE STATED THAT IT WAS SNOWING VERY HARD WHEN HE ARRIVED AT THE CABIN AROUND 1930.
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: instrument: helicopter; rotorcraft: helicopter
- Flight time: 3,267 hours in all; 287 in this make and model; 15 in the last 90 days; 8 in the last 30 days; 2,666 as pilot in command
- Medical certificate: Class 1 (valid medical--no waivers/lim.)
- Seat: rgt
The aircraft
- Last inspection: inspection type not recorded; 0 hours since
- Maximum gross weight: 7,055 lb
- Seats: 5
- Landing gear: fixed
- Engine: Lycoming LTS101-650B-1 (turboshaft); 0 hours total
The flight
- Departed from: Danville PA
- Destination: Sayre PA
- Runway 0
Weather at the time
- Light: night, dark
- Sky: not recorded
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 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.
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.