# NTSB FTW87FA198: Bell 206B, N33PW, Pledger, TX, August 12, 1987

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Field investigation · Final report
- Date: August 12, 1987, 16:20 local (21:20 UTC)
- Place: Pledger, TX
- Coordinates: 29.129449, -95.939033 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=29.1294&lon=-95.9390&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 4 uninjured
- Status: Completed, report April 24, 1989
- Report: Approved by Office Director
- NTSB case key (mKey): 22269
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW87FA198
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/22269/pdf
- Page: https://openairdocs.org/ntsb/FTW87FA198

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise - normal
  - rotor drive system,isolation link - failure,total (cause)
  - maintenance,inspection - inadequate, company maintenance personnel (contributing factor)
  - rotor drive system,engine to transmission drive - overtemperature (cause)
  - rotor drive system,engine to transmission drive - failure,total (cause)
- Forced landing, descent - emergency
  - autorotation
- Hard landing, landing - flare/touchdown
  - flare - improper, pilot in command (cause)

## Analysis

WHILE CRUISING AT 900' AGL, THE PLT NOTED A HVY SHUDDER FLWD BY A GRINDING NOISE, LOUD 'BANG' & A LOW ROTOR RPM SIGNAL. HE MADE AN AUTOROTATION TO A ROAD, BUT DRG TOUCHDOWN, THE MAIN ROTOR BLADES FLEXED DWN & SEVERED THE TAIL BOOM. AN EXAM REVEALED THE MAIN PWR (SHORT) SHAFT HAD FAILED DUE TO MISALIGNMENT & HI TEMPS RESULTING FROM THE MISALIGNMENT. FURTHER INV SHOWED THAT THE MISALIGNMENT WAS THE RESULT OF A FAILURE OF THE PYLON ISOLATOR MOUNT DUE TO DEBONDING BETWEEN THE UPPER PLATE & THE RUBBER DAMPER ELEMENT. DEBONDING OCCURRED AFTER PROLONGED EXPOSURE OF THE ISOLATOR MOUNT TO OIL & GREASE WHICH CHEMICALLY DETERIORATED THE BOND. THERE WAS EVIDENCE THE DETERIORATION HAD OCCURRED OVER A LONG PERIOD OF TIME. THE UNIT HAD BEEN INSPECTED PERIODICALLY, BUT THE IMPENDING FAILURE OF THE BOND HAD NOT BEEN DETECTED.

## Aircraft

- Registration: [N33PW](https://openairdocs.org/deregistered/N33PW-2015-05-19), registration cancelled 2015-05-19, S/N 2223, built 1977 (OpenAirDocs)
- Reported make and model: BELL 206B
- Registry model: [Bell 206B](https://openairdocs.org/model/bell-206b) (registry code 1181511) (OpenAirDocs)
- Registry engine: [Allison 250 SER 400HP](https://openairdocs.org/engine/allison-250-ser-400hp) (registry code 03013, turbo-shaft) (OpenAirDocs)
- Category: Helicopter
- Serial number: 2223
- Airframe hours: 4468
- Engines: ALLISON 250-C20B 317 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Part 135
- Operator: Houston Helicopters
- Registered owner: Notlet, Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: AAIP, August 1, 1986, 91 hours before
- Departed: BAY CITY, TX
- Destination: HOUSTON, TX
- Flight plan: Company VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 45; airline transport, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane, helicopter; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 8,826 total, 1,500 in this make and model, 8,375 as pilot in command, 82 in the last 90 days, 3 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 180° at 6 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 97 °F, dew point 70 °F
- Altimeter: 29.00 inHg
- Observed at: HOU, 25 nm away

## 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 19870812052269A](https://openairdocs.org/incident/19870812052269A), Aug 12, 1987: Bell 206B, Pledger, TX, Substantial damage. Autorotation on highway due to power loss. On landing,rotors severed tailboom. .main power shaft failed. Bolt fatigue

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.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.