Amateur-built MK-12 accident near Longmont, Colorado, May 18, 1984
On May 18, 1984 at about 4:35 pm local time, a amateur-built MK-12, registered N42JH, was destroyed in an accident near Longmont, Colorado (Longmont Muni airport). It was a personal flight under general aviation rules (Part 91). 1 person was killed. 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
- May 18, 1984 · about 4:35 pm local time
- Place
- Longmont, Colorado · Longmont Muni · map
- Type
- Accident
- Injuries
- 1 person was killed.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built MK-12
- Registration
- N42JH · registry record · serial 071
- Damage
- Destroyed
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
THE HOMEBUILT ACFT WAS ON DOWNWIND LEG OF THE TRAFFIC PATTERN, AFTER INITIAL TAKEOFF, WHEN IT WENT INTO A DIVE & COLLIDED WITH THE GROUND. A WITNESS SAID HE HEARD A POWER REDUCTION BEFORE THE DIVE & POWER ADDED AGAIN AS IT STARTED DOWN. THE PLT'S SON SAID HIS FATHER HAD CONTROL FLUTTER PROBLEMS AT SPEEDS ABOVE 100 MPH. THIS WAS VERIFIED BY A LOGBOOKENTRY. BY REDUCING SPEED, THE FLUTTER WENT AWAY. THUS, THE FLAPERON (AILERON) PUSH RODS WERE MODIFIED BY THE PLT. THE MODIFICATION CONSISTED OF A DOUBLER, 2 BEARINGS & A 1 INCH HOLE TO RETAIN THE BEARINGS. DURING A POST ACCIDENT INSPECTION, IT WAS FOUND THAT THE BELLCRANK ARM HAD SEPARATED FROM THE BEARING. IT WAS FOUND THAT THE DRILLED HOLE WAS IRREGULAR & LARGE ENOUGH TO ALLOW THE BEARING TO SLIP THRU THE HOLE. THE BEARING WAS THE ONLY MEANS OF RETAINING THE BELLCRANK TO THE FULCRUM POINT. THE RIGHT AILERON AT THE ACCIDENT SCENE WAS SEPARATED FROM THE MAIN WRECKAGE AND THE CONTROL PUSH RODS TO THE ELEVATOR WERE BROKEN AT THE BRACKET ATTACHED TO THE ELEVATOR.
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; single-engine land; instrument: airplane
- Flight time: 12,105 hours in all; 10 in this make and model; 143 in the last 90 days; 40 in the last 30 days
- Medical certificate: Class 1 (valid medical--w/ waivers/lim.)
- Seat: ctr
The aircraft
- Airframe total time: 104 hours
- Last inspection: annual inspection, October 18, 1983; 104 hours since
- Maximum gross weight: 366 lb
- Seats: 1
- Landing gear: fixed
- Engine: Jpx PUL 212 (piston); 0 hours total
The flight
- Flight plan: none
- Runway 11, 4,200 ft by 60 ft
Weather at the time
- Light: daylight
- Visibility: 75 statute miles
- Sky: clear
- Temperature: 82°F (28°C), dew point 0°F (-18°C)
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.
Other NTSB records under N42JH the same tail number, which may have belonged to a different aircraft at the time
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.