# NTSB CHI88FA091: Beech B90, N181LL, St. Paul, MN, April 5, 1988

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Field investigation · Final report
- Date: April 5, 1988, 15:15 local (20:15 UTC)
- Place: St. Paul, MN
- Coordinates: 44.929679, -93.080429 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=44.9297&lon=-93.0804&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 5 uninjured
- Status: Completed, report June 25, 1990
- Report: Approved by Office Director
- NTSB case key (mKey): 13939
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI88FA091
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/13939/pdf
- Page: https://openairdocs.org/ntsb/CHI88FA091

## Probable cause

MECHANICAL FAILURE AND STICKING OF THE PILOTS THUMB OPERATED TRIM SWITCH CAUSING NOSE DOWN PITCH COMMAND. THE FAILURE OF THE CABIN HEATER AND THE LOW CABIN TEMPERATURE ARE CONTRIBUTING FACTORS.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Altitude deviation,uncontrolled, cruise
  - electrical system,electric switch - failure,partial (cause)
  - remedial action - performed, pilot in command
  - air cond/heating/pressurization,cabin temp control - inoperative (contributing factor)
  - design stress limits of aircraft - exceeded (cause)

## Analysis

THE AIRPLANE WAS BEING OPERATED AS AN AIR AMBULANCE WHEN IT SUSTAINED SUBSTANTIAL DAMAGE DURING AN UNCOMMANDED HARD PITCHOVER. THE AIRPLANE WAS OPERATING IN VISUAL CONDITIONS ABOVE A SOLID CLOUD LAYER USING INSTRUMENT FLIGHT RULES. THE AIRPLANE RECOVERED FROM THE EXCURSION AND CONTINUED ON TO ITS DESTINATION. THE ATP RATED PILOT, THREE MEDICAL ATTENDANTS AND ONE PATIENT WERE NOT INJURED. TESTING OF THE PILOT'S WHEEL TRIM SWITCH SHOWED THE SWITCH WOULD STICK IN THE CLOSED OR ACTUATED POSITION AND NOT RETURN TO THE 'CENTER OFF' POSITION. THIS OCCURRED DURING TEMPERATURE CYCLING FROM ROOM TEMPERATURE TO BELOW FREEZING AND BACK AGAIN. THE CABIN HEATER HAD FAILED WITH AN OUTSIDE AIR TEMPERATURE OF -26 DEGS CELSIUS AND THE CABIN WAS COLD.

## Aircraft

- Registration: [N181LL](https://openairdocs.org/deregistered/N181LL-1991-04-09), registration cancelled 1991-04-09, S/N LJ440 (OpenAirDocs)
- Reported make and model: BEECH B90
- Registry model: [Beech B90](https://openairdocs.org/model/beech-b90) (registry code 1152912) (OpenAirDocs)
- Category: Airplane
- Serial number: LJ-440
- Airframe hours: 5950
- Engines: P&W PT6A-135 550 horsepower turbo prop
- Damage: Substantial damage
- Flight: Part 135
- Registered owner: Critical Care Inc.
- Airworthiness certificate: Standard, Normal
- Departed: MOT, MINOT, ND
- Destination: STP, ST. PAUL, MN
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 41; airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 5,005 total, 900 in this make and model, 2,800 as pilot in command, 20 in the last 90 days

## Weather

- Conditions: Instrument (IMC), Day
- Temperature: 18 °F, dew point -0 °F

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19880405069699A](https://openairdocs.org/incident/19880405069699A), Apr 5, 1988: Beech B90, St Paul, MN, Substantial damage. Uncommanded pitchover. Regained control after dive damaged airframe.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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