Incident Boeing 747-151 N607US, Thursday 13 May 1971

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Date:	Thursday 13 May 1971
Time:
Type:	Boeing 747-151
Owner/operator:	Northwest Airlines
Registration:	N607US
MSN:	19784/74
Year of manufacture:	1970
Engine model:	P&W JT9D-3A
Fatalities:	Fatalities: 0 / Occupants: 42
Other fatalities:	0
Aircraft damage:	Minor, repaired
Category:	Incident
Location:	near Honolulu Airport, HI (HNL) - United States of America
Phase:	Initial climb
Nature:	Passenger - Scheduled
Departure airport:	Honolulu Airport, HI (HNL)
Destination airport:	Tokyo
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
Northwest Airlines Flight 9, a Boeing 747-151,

During takeoff from Honolulu it was necessary to reduce power on the No. 3 and No. 4 engines from the predicted 1.395 to 1.33 engine pressure ratio in order to maintain exhaust gas temperature within operating limits. Power adjustment was also made during climb after takeoff for the same reason.
Shortly after takeoff, while the aircraft was in a right turn at 1,300 ft msl , a separation of the second-stage turbine disk occurred and pieces penetrated and ruptured the high-pressure turbine case and engine cowling.
A fire warning and severe vibration ensued which terminated following fire extinguisher discharge and engine shutdown procedures. Fuel jettison was accomplished to reduce weight to the maximum allowable for landing.
The flight returned to the Honolulu International Airport and landed safely. There were no injuries to passengers or crew.

The National Transportation Safety Board determines that the probable cause of this incident was the in-flight separation of the second-stage turbine disk of the No. 3 engine. The separation of the disk was the result of a fatigue crack which originated in a nickel-plated area of the reworked turbine air seal land and progressed into the base material under operating loads

Accident investigation: