Any vehicle must be lifted to allow us to get underneath or at least take the weight off the wheels. Our industry’s more normal vehicles, such as vans and pickups and even catering or servicing trucks like the ever-loved “Biffy” or lavatory trucks, are no real problem.
It’s only when you get up into the aircraft tugs designed to push and pull the wide-bodies that things become interesting.
It takes more than power to move the heavyweight aircraft and these tow units weigh upwards of 65,000 pounds. All that weight is needed to gain traction. And so here comes the weight, four-wheel drive and some heavy-duty rubber.
Even then, I have been disconcerted to have a tug lose traction and start moving sideways rather than in the desired direction. It really doesn’t take snow or ice to destroy traction. A little oil on the tarmac emulsified by some rain will do just fine.
WEIGHTY OR NOT
Weighty or not, these units must all be lifted. Sometimes just a corner to replace a wheel, but often to allow a lucky soul to slide underneath on a creeper to grease fittings or get to that pesky sump plug to drain engine oil. Only those working in the Northern climes can truly appreciate the delight of accumulated snow melting and falling on their faces.
Most all airline GSE shops have hydraulic lifts like those that can be found in any truck repair facility.
It goes without saying that anyone venturing under a jacked-up vehicle should install blocks or stands to prevent it coming down while they are underneath. I can also testify that these stands or props should be strong enough to hold the weight and also stable enough so they do not tip.
I came into the auto shop one dark and stormy night to get a cup of coffee and found a very white-faced Vinnie, the graveyard shift mechanic, contemplating a tractor that had rocked back off some wooden blocks that were being used to prop it up. It had come down. He had been just about to go under the tug to start dropping a tranny when he leaned on the vehicle. The wooden blocks toppled. He only had the front end up so it was not level. Vinnie was not a big person, but I’m not sure he would have neatly fit under the tug if it had come down on him.
In older facilities, servicing pits might be common. These make it simple to just drive the vehicle over the pit. Access was certainly good, better than being on your back under something that could flatten you if it came down prematurely.
Still, there is one hazard. Gasoline or cleaning agents produce fumes that are heavier than air and seek low points to collect in. Servicing pits under often leaking vehicles provide just such a spot. If ignited servicing pits are very hard to escape from and so the Occupational Safety and Health Administration, as well as fire protection codes, have some stiff requirements.
Aircraft are a special matter. Our most common and abused aircraft jack is the axle jack used to change wheels and brakes. These jacks live out on the ramp and are exposed to weather. That’s bad enough, but they’re also exposed to aircraft hydraulic fluid that drips down on them at exactly the same time their pistons are extended.
Jacks commonly use a mineral fluid and their seals are often not compatible with the synthetic aircraft hydraulic fluids. On several notable occasions I have had axle jacks blow their seals out while extended with an aircraft on top of them. They were fitted with locking rings that screwed down on the hydraulic ram. When the aircraft axles were up, prior to changing the wheel, you screwed a locking ring down on the lifting ram. To release the lock you had to slightly extend the ram to take the weight off the locking ring. Inevitably, the ram seals would then blow their guts.
It takes a wing jack to lift the airplane enough to get the axle jack out and these are usually miles away at the hangar. Towing them on their casters is out so we had to use a large forklift to transport them. Try that one on the long service road around JFK Airport.
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