History of the flight
Approximately 21 minutes after departure while the Boeing 767 was passing through flight level (FL) 285 on climb to FL310, a loud bang sound was heard from the right engine. Cabin crew and passengers reported a flash and sparks from the rear of the engine. The pilot reported an immediate drop in the right engine pressure ratio (EPR) and a rise in the exhaust gas temperature (EGT). A moderate vibration was felt through the airframe.
The crew actioned the engine surge/stall checklist but as the EGT continued to increase, the engine severe damage/separation checklist was actioned and the right engine was shut down. The engine fire bottles were not discharged.
The crew made a PAN call stating that the right engine had failed and requested a descent to FL240 and a return to Sydney. The pilot reduced speed to 240 kts in an attempt to reduce the vibration. However, the vibration reduced only during the final approach.
An inspection of the right engine revealed that about one-quarter of the no. 28 fan blade had broken away, resulting in substantial damage to the inside of the nose cowl and to the majority of the fan blades. Abnormal displacement of fan blades (shingling) was evident on the mid-span shrouds of a number of blades surrounding the fractured blade.
The fan blade attrition lining was damaged around its entire circumference as a result of heavy fan blade rub. The forward fan case was distorted with five nose cowl attachment points damaged.
The nose cowl internal acoustic liners were damaged through to the outer skin in several locations with two punctures of the nose cowl outer skin. The nose cowl had shifted forward, creating a gap between the nose cowl and the forward fan case flange. Fan blade debris and the mid-span shroud root section of the fractured blade were found embedded in the nose cowl following removal of cowl access panels.
Fan blade maintenance
Operator maintenance records indicated that the right engine fan blades were inspected for leading edge cracks on 13 March 1999 (93 hours and 54 cycles prior to the incident). No indications of cracks were detected at that time. Routine inspections of the fan blade leading edges for cracks had been carried out on a monthly basis. A vibration survey test was carried out on 2 February 1999 after removal and inspection of two fan blades.
In the 9 months before the incident, 13 fan blades on the right engine were found to have incurred foreign object damage. These blades had been blend repaired and inspected for cracks. The fractured fan blade was not one of those blades.
The operator reported that fan blade leading edge restoration was carried out at a 5,000 cycle interval or at 3,000 cycles should an overhaul opportunity occur. Lubrication of the mid-span shroud to help prevent shroud lockup was not required while the engine was fitted to an aircraft (on-wing). The fan blades were overhauled 6,689 hours / 3,889 cycles before this incident.
The fractured fan blade and several liberated portions of the blade were examined by the ATSB and by the engine manufacturer. The other 39 fan blades were returned to the engine manufacturer for review.
The blade had fractured about 470 mm above the blade platform, just inboard of the mid-span shroud. About one-quarter of the blade had been liberated. The fan blade had fractured as a result of fatigue crack growth. The failure had originated at a foreign object damage impact site 2.54 mm aft of the blade leading edge on the rear (concave) face of the blade. Traces of mineral debris were detected at the crack origin, indicating that the foreign object damage was the result of stone ingestion. Fatigue crack growth, from a crack depth of 1.5 mm, probably occurred over about 35 flight cycles. The blade had no material abnormalities at the fracture site. No evidence of a birdstrike was found.
The fractured blade had an eroded leading edge in the mid-span shroud region of the fan blade. The engine manufacturer reported that all of the fan blades had eroded leading edges in front of the mid-span shroud (about 152 mm above and below the shroud), and that the shroud hardfaces showed signs of possible lockup. It could not be determined whether the shroud lockup had occurred before or after the fan blade fracture.
The cracking and fracture of the fan blade appeared to be the result of high stress at a foreign object damage impact location in combination with vibratory stress and possible locked shrouds. The manufacturer reported that an adverse combination of these items could produce stresses high enough to fracture a fan blade. The eroded leading edge evident on all fan blades would have contributed to the blade fracture by affecting the vibratory characteristics of the fan blades.
The engine manufacturer said there had been only one other reported fracture of this type of fan blade. This was also due to fatigue crack growth starting at a foreign object damage impact site at a similar radial location to this fracture.
- A fan blade of the right engine fractured as a result of fatigue crack growth during aircraft climb, resulting in shutdown of the engine.
- The crack originated at a foreign object damage impact site on the rear face of the blade near the mid-span shroud.
- All fan blades of the right engine had significant leading edge erosion/blunting in the mid-span shroud region.
- The fan blade shroud hardfaces showed signs of shroud lockup.
- High stress at the foreign object damage impact site, vibratory stresses due to blade leading edge erosion and possible locked shrouds caused the crack to grow.
- Liberation of one-quarter of the fan blade and the resulting fan imbalance damaged the fan case, nose cowl and other fan blades.
As a result of the fan blade fracture, the engine manufacturer and operator took safety action to address shroud lockup, leading edge erosion and blade foreign object damage.
- The manufacturer issued service information on fan blade shroud lubrication and recommended that lubrication of the fan blade shroud hardface surfaces be performed at every "A" check. The manufacturer revised the JT9D-7R4 Engine Maintenance Manuals to incorporate the lubrication procedure. No on-wing shroud lubrication had previously been required.
- The operator incorporated the fan blade shroud lubrication procedure into their Maintenance Manual. Lubrication of the fan blade shrouds is to be carried out after a compressor wash, both on-wing and in the test cell, and during workshop assembly.
Fan blade leading edge erosion
- The manufacturer recommended that the operator maintain proper leading edge contours on all fan blades as per the Engine Manual, and that leading edge restoration be performed between 2,000-3,000 cycles, with a 5,000 cycle maximum time between refurbishment.
- The operator commenced a program to recontour the fan blade leading edges as per the Engine Manual every 2,500 cycles. Procedures were put in place to monitor and track the time and removal of fan blade sets reaching the 2,500 cycle threshold. A set of float fan blades and tooling was ordered to support the program.
Foreign object damage inspection
- The manufacturer recommended that the operator inspect fan blades for foreign object damage in accordance with the maintenance manual.
- The operator advised that a routine visual inspection for foreign object damage as per the maintenance manual was already in place and was conducted every 200 cycles. An eddy current inspection of the fan blade leading edge is performed every 350 airframe hours.
- Immediately following the fan blade failure, the operator conducted a close visual and eddy current inspection of all Boeing 767 engine fan blades. A number of damaged fan blades were found and corrective action taken.
|Date:||22 March 1999||Investigation status:||Completed|
|Time:||1946 hours ESuT|
|Location:||56 km E Cowra, (NDB)||Investigation type:||Occurrence Investigation|
|State:||New South Wales||Occurrence type:||Abnormal engine indications|
|Release date:||22 November 2000||Occurrence class:||Technical|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Minor|
|Departure point||Sydney, NSW|
|Departure time||1910 hours ESuT|