N141UA collided with 737 tail

N141UA 747SP United ( c/n: 21023 )

Brief

2 mechanics taxiied the United 747SP from a terminal gate to maintenance and the right wing hit the tail of a B737 which was lined up on a parallell taxiiway waiting for departure.

Analysis

A BOEING 747SP COLLIDED WITH THE TAIL OF A BOEING 737.
THE 737 WAS LINED UP ON A PARALLEL TAXIWAY AWAITING DEPARTURE.
THE 747 WAS TAXIING FROM A TERMINAL GATE TO MAINTENANCE. THE 747 WAS BEING OPERATED BY TWO MECHANICS. ONE OF THE MECHANICS WAS NOT QUALIFIED TO TAXI THE 747.

NO. 4 ENG HUNG START AND WAS NOT RUNNING DURING TAXI. THE NO. 4 ENG HYD SYS WAS SWITCHED OFF. THE NO. 4 HYD SYS IS THE PRIMARY POWER FOR THE ACFT BRAKE SYS. THE 747’S INERTIAL NAV SYS (INS) IS REQUIRED TO OPERATE WHILE TAXIING FOR SPEED REFERENCE. THE INS WAS ALSO SWITCHED OFF.

THE 747 SPEED BECAME EXCESSIVE ON PARALLEL TAXIWAY. WHEN MECH ATTEMPTED TO STOP THERE WAS NO BRAKE POWER.
HE DID NOT ACTIVATE THE EMER BRAKE SYS POWERED BY NO. 2 ENG HYD SYS. THE MECH SWERVED THE 747 TO THE LEFT. THE 747 R WING COLLIDED WITH TAIL OF 737.

THE AIRLINE MAINT SUPERVISOR OF 747’S WAS AWARE OF MECH NON-QUAL AND OF THE NO. 4 ENG NOT OPERATING. DECISION WAS MADE TO LET THE ACFT TAXI CONTRARY TO PROCEDURES.

Probable Cause

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
FAILURE OF THE QUALIFIED MECHANIC TO INSURE THE OPERATION OF THE AIRCRAFT BRAKES PRIOR TO TAXIING AND HIS FAILURE TO UTILIZE THE EMERGENCY BRAKE SYSTEM TO PREVENT THE COLLISION. CONTRIBUTING TO THIS ACCIDENT WAS THE DECISION OF AIRLINE MAINTENCE SUPERVISORS TO ALLOW A NON QUALIFIED MECHANIC TO PERFORM RIGHT SEAT/FLIGHT ENGINEER PANEL DUTIES. ALSO CONTRIBUTING WAS THE QUALIFIED MECHANICS FAILURE TO USE THE AIRCRAFT’S INERTIAL NAVIGATION SYSTEM FOR CROSS REFERENCE TO TAXI SPEED.

Findings

Occurrence #1: ON GROUND/WATER COLLISION WITH OBJECT
Phase of Operation: TAXI

Findings
1. (C) AIRCRAFT HANDLING – IMPROPER – UNQUALIFIED PERSON
2. (F) OPERATION WITH KNOWN DEFICIENCIES IN EQUIPMENT – PERFORMED – COMPANY MAINTENANCE PERSONNEL
3. (F) NAVIGATION COMPUTER – NOT USED – COMPANY MAINTENANCE PERSONNEL
4. (F) HYDRAULIC SYSTEM – NOT UNDERSTOOD – COMPANY MAINTENANCE PERSONNEL
5. (C) BRAKES(NORMAL) – INADVERTENT DEACTIVATION – COMPANY MAINTENANCE PERSONNEL
6. (C) BRAKES(EMERGENCY) – NOT USED – COMPANY MAINTENANCE PERSONNEL

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Read Full Report (pdf)
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Read Brief Report (pdf)
Source: NTSB

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Tommy Mogren
Tommy Mogrenhttp://www.747sp.com
Passion 4 Aviation and the 747SP in particular. Photographer and video producer. YouTube | Viking Wings

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