Boeing B747 HS-VAC

Summary

On 5 July 2008, a Boeing B747 registered HS-VAC, operated by Saudi Arabian Airlines, was involved in an incident near Jeddah, Saudi Arabia. The number of people on board was not recorded. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

5 July 2008

Classification

Incident

Location

Jeddah, Saudi Arabia

Coordinates

Not recorded

Aircraft

Boeing B747

Registration

HS-VAC

Category

Airplane

Operator

Saudi Arabian Airlines

Operating rule

Part 129: Foreign

Phase of flight

Not recorded

Route

Jeddah → Jakarta

Aircraft damage

Minor

NTSB number

ENG08IA030

Injuries not recorded.

Failure of the low pressure turbine stage 3 disk due to a design that is vulnerable to high pressure turbine unbalance-induced synchronous vibration that cannot be detected in flight, and the subsequent uncontained engine failure.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The airplane made an air turnback and successful landing following an uncontained No. 1 engine failure during initial climb after takeoff. There was minor impact damage to the airplane's left wing and flaps. The No. 1 engine low pressure turbine (LPT) case had separated circumferentially in plane with the stage 3 (S3) LPT turbine, and the engine components aft of the separation were liberated. A high pressure turbine (HPT) borescope inspection found localized airfoil damage sufficient to result in HPT rotor unbalance. HPT rotor unbalance-induced synchronous vibration forces interacted with the engine LPT rotor system through a common bearing support and excited a bladed-disk mode response in the LPT S3 disk. The resonant amplitude of the alternating stress experienced by the disk resulted in bending loads exceeding the material endurance limit, and high cycle/high amplitude fatigue cracks initiated along the LPT S3 disk forward spacer arm rim diameter. Once initiated, the cracks propagated rapidly through the spacer arm thickness and the individual cracks joined to form a single circumferential crack, resulting in the separation of the disk at the forward spacer arm. The freed aft portion of the LPT rotor accelerated and penetrated the engine case, releasing high-energy debris as disk fragments and all of the engine components aft of the LPT S3 nozzles were liberated. NTSB Safety Recommendations A-10-98 and A-10-99 (Urgent); A-10-100, and A-10-101 were published in connection with this investigation. For further information about these recommendations, see NTSB case number ENG09IA004.

Quoted verbatim from the NTSB record.