# NTSB DEN93IA027: Boeing 757-222, N508UA, Grand Junction, CO, February 14, 1993

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: February 13, 1993, 19:15 local (Feb 14, 1993, 02:15 UTC)
- Place: Grand Junction, CO
- Coordinates: 39.109409, -108.529991 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.1094&lon=-108.5300&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 47 uninjured
- Status: Completed, report November 3, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 18252
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN93IA027
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18252/pdf
- Page: https://openairdocs.org/ntsb/DEN93IA027

## Probable cause

FAILURE OF THE LEFT GENERATOR CONTROL UNIT (GCU), INTEGRATED DRIVE GENERATOR (IDG), RIGHT (SIDE) ENGINE INDICATOR AND CREW ALERT SYSTEM (EICAS), AND BUS TIE BAR (BTB).

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise - normal
  - electrical system,generator - shorted (cause)
  - warning system(other) - shorted (cause)
  - autopilot/flight director - disengaged
  - autopilot/flight director,auto throttle - disengaged
  - flight/nav instruments,horiz situation ind(hsi) - failure,total
  - flight/nav instruments,attitude director ind(adi) - failure,total
  - flight compartment light(s) - erratic

## Analysis

WHILE CRUISING AT FL390, THE AUTOTHROTTLES AND AUTOPILOT DISENGAGED, THE CAPTAIN'S INSTRUMENTS FAILED, AND THE COCKPIT LIGHTING CYCLED ON AND OFF. THE LEFT GENERATOR LIGHT ILLUMINATED, THE EICAS FAILED, A CYCLIC BANGING WAS HEARD, AND AN ACRID ODOR WAS NOTICEABLE.  THE LEFT AC BUS AND TRANSFER BUS WERE DEENERGIZED AND THE CAPTAIN ELECTED TO DIVERT TO THE NEAREST SUITABLE AIRPORT.  POST INCIDENT INVESTIGATION DISCLOSED A SHORTED DIODE IS THE LEFT GCU (GENERATOR CONTROL UNIT), A DEFECTIVE IDG (INTEGRATED DRIVE GENERATOR), A SHORT IN THE INPUT POWER FILTER IN THE EICAS (ENGINE INDICATOR AND CREW ALERT SYSTEM), AND A DEFECTIVE BTB (BUS TIE BAR).

## Aircraft

- Registration: [N508UA](https://openairdocs.org/aircraft/N508UA), registered now, S/N 24744, built 1990 (OpenAirDocs)
- Reported make and model: BOEING 757-222
- Registry model: [Boeing 757-222](https://openairdocs.org/model/boeing-757-222) (registry code 1384956) (OpenAirDocs)
- Registry engine: [Pratt & Whitney PW2040](https://openairdocs.org/engine/pratt-whitney-pw2040) (registry code 52121, turbo-fan) (OpenAirDocs)
- Category: Airplane
- Serial number: 24744
- Airframe hours: 9483
- Engines: P&W 2037-717 37000 lbs thrust turbo fan
- Damage: No damage
- Flight: Part 121
- Operator: United Airlines
- Registered owner: United Airlines
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, January 14, 1993, 284 hours before
- Departed: PHL, PHILADELPHIA, PA
- Destination: LAX, LOS ANGELES, CA
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 58; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 11,698 total, 410 in this make and model, 155 in the last 90 days, 59 in the last 30 days

## Weather

- Conditions: Visual (VMC), Night/dark
- Wind: 320° at 5 knots
- Visibility: 30 statute miles
- Lowest ceiling: none
- Temperature: 32 °F, dew point 21 °F
- Altimeter: 30.00 inHg

## FAA reports on this event (1)

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

- [Incident 19930213006269I](https://openairdocs.org/incident/19930213006269I), Feb 13, 1993: Boeing 757222, Grand Junction, CO. Left generator off line. Acrid odor. APU started. Diverted to Grand juction.

## Other investigations on N508UA (2)

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.

- [NTSB SEA08LA061](https://openairdocs.org/ntsb/SEA08LA061), Jan 14, 2008: Boeing 757-222 (N508UA), San Francisco, CA, substantial damage. Probable cause: The company tug operator's failure to maintain clearance with another aircraft during the pushback process. Also causal was the ground controller's failure to alert the pilot of the other aircraft…
- [NTSB DEN93LA098](https://openairdocs.org/ntsb/DEN93LA098), Aug 2, 1993: Boeing 757-222 (N508UA), Denver, CO, substantial damage. Probable cause: THE FIRST OFFICER'S IMPROPER RECOVERY FROM A BOUNCED LANDING. FACTORS WERE: THE FIRST OFFICER'S DELAYED INITIATION OF THE FLARE, AND THE CAPTAIN'S IMPROPER SUPERVISION OF THE FLIGHT.

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.