Cessna 421A accident near Helena, Montana, February 4, 1988
On February 4, 1988 at about 3:00 am local time, a Cessna 421A, registered N517S, was destroyed in an accident near Helena, Montana (Helena Regional airport). It was a flight of an unrecorded kind under charter and air-taxi rules (Part 135). 3 people were killed. The weather was instrument conditions (cloud, fog or low visibility).
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
- February 4, 1988 · about 3:00 am local time
- Place
- Helena, Montana · Helena Regional · map
- Type
- Accident
- Injuries
- 3 people were killed.
- Weather
- instrument conditions (cloud, fog or low visibility)
- Aircraft
- Cessna 421A · all 421As on the register
- Registration
- N517S · registry record · serial 421A002
- Damage
- Destroyed
- Flight
- Flight of an unrecorded kind · charter and air-taxi rules (Part 135)
The NTSB's narrative final · quoted from the NTSB record
THIS ACCIDENT OCCURRED DURING A NIGHT, ILS APP TO RWY 27 IN IMC. THE ACFT COLLIDED WITH A MOUNTAIN 12 NM ESE OF THE ARPT WHILE TURNING INBOUND TO INTERCEPT THE LOC COURSE. INVESTIGATION REVEALED THAT ONE VOR RECEIVER WAS SET ON THE DESTINATON ILS FREQ, THE SECOND VOR WAS SET ON AN EN ROUTE VOR 51 NM WEST OF THE DESTINATION ARPT, AND THE DME RADIO, A SEPARATE TRANSCEIVER, WAS SET ON THE DESTINATION DME TRANSMITTER. THE FREQS OF THE EN ROUTE VOR AND THE DESTINATION VOR WERE 117.1 AND 117.7, RESPECTIVELY. THE OUTBOUND COURSE FOR THE ILS APP PROCEDURE WAS 088 DEG AND THE ACDT SITE WAS LOCATED ON THE 088 RADIAL OF THE EN ROUTE VOR. INVESTIGATION ALSO REVEALED THAT THE PIC WAS OCCUPYING THE RT FRONT SEAT AND AN EXPERIENCED PLT WHO WAS NOT CURRENT IN THIS AIRCRAFT WAS OCCUPYING THE LEFT SEAT. THE SECOND VOR RECEIVER CONTROL HEAD WAS LOCATED IN THE LOWER RIGHT PORTION OF THE INST PANEL, IN A LOCATION WHERE THE SELECTED FREQ WAS DIFFICULT TO READ.
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
- Ratings: multi-engine land; multi-engine sea; single-engine land; single-engine sea; instructor: airplane multi-engine; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane
- Flight time: 4,900 hours in all; 119 in this make and model; 35 in the last 90 days; 35 in the last 30 days; 4,503 as pilot in command; 567 on instruments
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: rgt
The aircraft
- Airframe total time: 4,758 hours
- Last inspection: 100-hour inspection, December 8, 1987; 22 hours since
- Maximum gross weight: 6,840 lb
- Seats: 3
- Landing gear: retractable
- Engine: Continental GTSIO-520-D (piston); 0 hours total
- Fire on the ground
- Operator: Minuteman Aviation
The flight
- Departed from: MSO Missoula MT at 2:17 am
- Destination: HLN Helena MT
- Flight plan: IFR
- Runway 27, 9,000 ft by 150 ft
- A second pilot was aboard
Weather at the time
- Light: night, dark
- Sky: not recorded; not recorded
- Temperature: 27°F (-3°C), dew point 19°F (-7°C)
- Altimeter: 30.00 inHg
- Observation at 2:53 am from HLN, 12 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 2 | |||
| Passengers | 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.