Date: 201304
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight phase: Parked
Aircraft component: Landing Gear
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Lead Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural FAR; Ground Event / Encounter Loss Of Aircraft Control
Detector: Person Maintenance
When detected: Aircraft In Service At Gate
Result: Aircraft Aircraft Damaged; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Company Policy; Aircraft; Human Factors; Weather; Procedure
Primary problem: Company Policy

Narrative: Two company maintenance technicians were assigned to move an empty aircraft from the International Terminal to the Domestic Terminal for an outbound flight. One Mechanic had just entered aircraft as the other unplugged the jetway power in preparation for a high speed tow operation. Just as the Mechanic detached the power cord; a gust of wind caused the aircraft to 'weather vane' at the gate. The aircraft pivoted on the main landing gear and the nose of the aircraft went into an uncontrolled excursion of between twenty five and forty feet. Neither Mechanic was injured. The main gear and nose gear were all chocked. The main gear chocks were simply displaced by the tires. The nose gear chocks were not displaced; but had no effect on the lateral movement of the [aircraft] excursion. The aircraft was removed from revenue service and taken to a hangar for inspection. This is the third incidence in several months of company aircraft 'weather vaning' at a gate. A previous incident pulled an attached tow tractor along with the aircraft. My Air Carrier has a new policy of 'brakes off;' when an aircraft is in a gate. Most other air carriers do not allow brakes off at a gate. My Air Carrier has only recently instituted such a policy in order to facilitate a faster movement of aircraft without the necessity of a person in the cockpit. It may work fine in [some locations]; but should not be promoted in [very] windy locations. My Air Carrier says they have a policy of setting the brakes in high winds; but these conditions are transient and conditional; and therefore have no place as a policy when adverse weather conditions pop up at random times. Aircraft can also be 'weather vaned' by [other] aircraft [movement] at breakaway thrust.  This potentially dangerous aircraft handling practice can only be resolved by consistently setting aircraft brakes  at all times when an aircraft is in the gate.

Callback: Reporter stated this has happened a few times. Flight crews are directed to release brakes at the gates as soon as the wheels are chocked signal is given.  The reporter stated B737 Next Generation aircraft seem to be more susceptible to being 'weather-vaned;' probably due to the longer fuselage; lighter aircraft and large tail section. The situation is dangerous and financially costly. If any of their airplanes are 'weather-vaned;' they are considered unserviceable. The aircraft will be removed from service; taken to the hangar and have a side-Load structural inspection accomplished; especially on the landing gears.  The fuselage; wings and engines are also inspected. These incidents are happening even though all the aircraft wheels were chocked.  The aircraft in his report had wing damage from contacting ground equipment when the aircraft 'weather-vaned.'  Fortunately; the aircraft was empty and no one was injured.Reporter stated the recent company policy of leaving the brakes off at terminal gates was not just to cool-down brakes; but was also set-up to help expedite movement of aircraft between gates by ramp personnel who are not qualified to operate aircraft brakes; components or systems.  He believes that policy increases the potential for mistakes in an already dangerous terminal gate work environment; especially since maintenance and other personnel may still be working on; or around; the same aircraft. With miscommunication and lack of adequate multi-shift turnover information already an issue between shifts and with other groups working aircraft at terminal gates; he doesn't see how these two new policies and practices are going to make their operations safer. He does not know if brakes are set during passenger boarding.



Synopsis: A Lead Mechanic reports how company policy of requiring 'brakes-Off' on aircraft at domestic and international terminals; has contributed to multiple incidents in one month; of aircraft that 'weather-vaned' off the gates due to windy conditions. B737NG aircraft appear to be more susceptible.