B737-800
Maintenance Airframe; Maintenance Powerplant
Maintenance Inspector 9; Maintenance Technician 12
Distraction; Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Critical
General Maintenance Action
Company Policy; Human Factors; Equipment / Tooling
During straightforward tow into hangar after 'high speed distance' tow (faster than walking speed and approximately 1/4 mile from gate to hangar). I was doing a Line Operations Safety Assessment (LOSA) observation of this movement when approximately 50 FT from park; the towbar broke it's 'shear' bolt; causing erratic nose gear movement. Brakes were applied; towbar removed and nose gear inspected for damage. After inspection; serviceable towbar was installed and tow continued without incident. Tow tractor that local Maintenance Director wants used for 'distance' towing is a TUG GT50H (B777 Tractor). Towbar used is manufactured by XXX Industries. Local Mechanic called XXX Industries yesterday; due to disconnects during towing that have occurred three-times. XXX Industries states they have never sold the B737NG towbar with (different head; latching mechanism; and greater tensile shear bolt) to our Air Carrier. We have a Classic B737 towbar for B737-100/200/300/500 aircraft which are half the weight of the B737-900ER (90;600 LBS empty). Also; tow tractor is high profile [shape-design] and only portion viewed [from the cab of the tug] during the tow is [the aircraft's] radome and wingtips. [Tug Rider] passenger must stand to view [aircraft's] maximum Turn Radius Indicator (red stripe) and give direction to the Driver. I filed a LOSA observation for this incident and sent towbar out for repair. Although this incident resulted in tooling damage; soon it will be aircraft or personnel if correct Ground Support Equipment (GSE) is not afforded. Tractor is not a covered 'hood' type. Three technicians have incurred 'jet blast' from other aircraft while towing on taxiways. Monthly safety meeting was conducted two days prior to this event; all of the 15-members that were present agreed that this GSE towing practice is unsafe; but Director has not halted its practice. Technicians feel threatened for their career due to previous 'firing' comments if safety isn't followed. Equipment unsafe; unreliable and no instructions.
Reporter stated their Station had been using a towbar not designed for their heavier B737NG aircraft. Towbars for the lighter weight; Classic B737s will easily attach to the tow lug on the Nose Landing Gear (NLG) of the heavier B737NG aircraft. He has also seen Maintenance use B737NG towbars on Airbus aircraft.Reporter stated that midnight mechanics had previously taxied aircraft to the hangar prior to the recent arrival of their new local Maintenance Director. He immediately mandated no more taxiing of aircraft. Mechanics did not want to tow aircraft in cold freezing weather; blinding snow or pouring rain. All of the tow tugs had the protective enclosures for the cabs removed; after Ramp started moving aircraft; leaving Midnight mechanics only 'open-air' cabs to tow aircraft with. Most mechanics on midnight shift were unfamilar with the airfield and had never towed an aircraft. Performing high-speed towing of the heavier B737NG aircraft with lighter tugs also caused the tug transmissions to overheat. The heavier TUG GT50 models could do the high speed tow; but were extremely difficult to maneuver in tight turns; especially when moving aircraft 'in' and 'out' of the hangar. Mechanics would taxi right up to the hangar entrance and hook-up a smaller tug to pull the B737s into the hangar. Now they use the GT50 heavy tractor to tow to the hangar; then disconnect the tractor and hook-up the smaller tractor. Reporter stated the new Maintenance Director has finally agreed to get two of the GT50 tow tractors refurbished with protective enclosures. XXX Industries did come in and performed a maintenance service on all of their towbars; many of which had bushing inserts missing from where the shear pins were installed in the towbar head that attaches to the NLG tow lug fitting. Many of the Locking handles on the towbar head for securing the towbar to the NLG tow fitting had very low foot-pound tension and could easily be flipped out of the 'locking' position; allowing the towbar head to disengage on at least one side of the NLG tow fitting.
An Aircraft Maintenance Technician (AMT) describes some of his observations and safety concerns involving recent tow bar disconnections that have occurred during towing of B737-800 aircraft and the difficulty viewing the same aircraft when using large tow tractors.