Sikorsky S-76A accident near Unionville, Pennsylvania, September 22, 1984
On September 22, 1984 at about 3:30 pm local time, a Sikorsky S-76A (helicopter), registered N79K, was substantially damaged in an accident near Unionville, Pennsylvania. It was a flight of an unrecorded kind under charter and air-taxi rules (Part 135). No one was hurt; 8 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The NTSB has not yet published a probable cause for this accident. Investigations usually take one to two years; this page updates when the final report is released.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 22, 1984 · about 3:30 pm local time
- Place
- Unionville, Pennsylvania · map
- Type
- Accident
- Injuries
- No one was hurt; 8 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Sikorsky S-76A · all S-76As on the register
- Registration
- N79K · registry record · serial 760098
- Damage
- Substantial damage
- Flight
- Flight of an unrecorded kind · charter and air-taxi rules (Part 135)
The NTSB's narrative final · quoted from the NTSB record
ON APPROACH, ACFT YAWED RIGHT. PLT REDUCED POWER AND EXECUTED EMERG LNDG. BEFORE SHUTDOWN, IT WAS NOTED THE T/R WAS STATIONARY WHILE THE MAIN ROTOR CONTINUED TO TURN. INVESTIGATION REVEALED T/R DRIVE SHAFT HAD SEPARTED DUE TO THERMAL/MECHANICAL DAMAGE INCURRED BY CONTACT WITH ENGINE FIREWALL. FURTHER INVESTIGATION REVEALED THAT A FIREWALL MODIFICATION HAD BEEN DESIGNED WHICH INCLUDED A DOUBLER STRIP AT THE FWD AND AFT FIREWALL SECTION CONNECTION. PRESENCE OF DOUBLER WOULD DECREASE CLRNC BETWEEN FIREWALL AND T/R SHAFT. IT WAS FURTHER DETERMINED THAT, DURING INSTALLATION, THE FWD FIREWALL SECTION, TO WHICH THE DOUBLER IS ATTACHED, WAS MISPOSITIONED WITH RESULT THAT CLRNC WAS REDUCED TO NIL. COMPONENTS CAME INTO CONTACT DURING OPERATIONS.
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: single-engine land; instructor: helicopter; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Medical certificate: Class 1 (valid medical--no waivers/lim.)
- Seat: rgt
The aircraft
- Airframe total time: 1,786 hours
- Last inspection: 100-hour inspection, June 30, 1984; 100 hours since
- Maximum gross weight: 7,500 lb
- Seats: 8
- Landing gear: retractable
- Engine: Allison A250C30S (turboshaft); 0 hours total
The flight
- Departed from: 40N Coatesville PA at 3:30 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 160° at 3 knots
- Visibility: 10 statute miles
- Sky: scat at 10,000 ft
- Temperature: 70°F (21°C), dew point 52°F (11°C)
- Altimeter: 30.00 inHg
- Observation at 2:51 pm from PNE
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 2 | |||
| Passengers | 6 |
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.