Narrative:
The re-engined turboprop Otter was performing a test flight maneuvers when problems with the modified fuel system occurred. Ice blocking a fuel vent line caused a partial collapse of the main (engine feed) fuel cell which produced an erroneous fuel quantity reading. In addition, the main tank overflow shutoff valve was leaking, so tank overflow occurred. The fuel overflow caution light illuminated and auxiliary tank fuel pump feed to main automatically shut down. Due to miscalibration, this system overrode pilot attempts to restart aux fuel pumps. The pilot remained in test area troubleshooting rather than an immediate return to base. He finally noted main tank gauge continued to read 'full.' En route to Boeing Field, fuel starvation occurred. He attempted a forced landing in a small athletic field in a residential area rather than ditch in Puget Sound. The aircraft touched down, then bounced across an adjacent street. The arresting action of telephone wires on the vertical fin brought the aircraft to rest in a residential backyard.
PROBABLE CAUSE:
fuel system,vent..blocked(total)
fluid,fuel..starvation
CONTRIBUTING FACTORS:
precautionary landing..delayed..pilot in command
terrain condition..none suitable
fuel supply..misjudged..pilot in command
fuel system,tank..distorted
engine instruments,fuel quantity gage..false indication
fuel system,fuel shutoff..leak
Forced landing outside airport
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
| Status: | Accident investigation report completed and information captured |
| Date: | Wednesday 19 December 1984 |
| Time: | 11:08 |
| Type: |  de Havilland Canada DHC-3T Cox Turbine Otter |
| Operator: | Cox Aircraft Corp. |
| Registration: | N4247A |
| MSN: | 421 |
| First flight: | 1964 |
| Total airframe hrs: | 7445 |
| Engines: | 1 Pratt & Whitney Canada PT6A-135 |
| Crew: | Fatalities: 0 / Occupants: 1 |
| Passengers: | Fatalities: 0 / Occupants: 2 |
| Total: | Fatalities: 0 / Occupants: 3 |
| Aircraft damage: | Substantial |
| Aircraft fate: | Written off (damaged beyond repair) |
| Location: | Alki Point, Seattle, WA ( United States of America)
|
| Phase: | En route (ENR) |
| Nature: | Test |
| Departure airport: | Seattle-Boeing Field International Airport, WA (BFI/KBFI), United States of America |
| Seattle-Boeing Field International Airport, WA (BFI/KBFI), United States of America |
The re-engined turboprop Otter was performing a test flight maneuvers when problems with the modified fuel system occurred. Ice blocking a fuel vent line caused a partial collapse of the main (engine feed) fuel cell which produced an erroneous fuel quantity reading. In addition, the main tank overflow shutoff valve was leaking, so tank overflow occurred. The fuel overflow caution light illuminated and auxiliary tank fuel pump feed to main automatically shut down. Due to miscalibration, this system overrode pilot attempts to restart aux fuel pumps. The pilot remained in test area troubleshooting rather than an immediate return to base. He finally noted main tank gauge continued to read 'full.' En route to Boeing Field, fuel starvation occurred. He attempted a forced landing in a small athletic field in a residential area rather than ditch in Puget Sound. The aircraft touched down, then bounced across an adjacent street. The arresting action of telephone wires on the vertical fin brought the aircraft to rest in a residential backyard.
Probable Cause:
PROBABLE CAUSE:
fuel system,vent..blocked(total)
fluid,fuel..starvation
CONTRIBUTING FACTORS:
precautionary landing..delayed..pilot in command
terrain condition..none suitable
fuel supply..misjudged..pilot in command
fuel system,tank..distorted
engine instruments,fuel quantity gage..false indication
fuel system,fuel shutoff..leak
Classification:
Fuel starvationForced landing outside airport
Sources:
» NTSBPhotos
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
accident date: 19-12-1984
type: de Havilland Canada DHC-3T Cox Turbine Otter
registration: N4247A
Map
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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