TOWBARS

AIRCRAFT TOWBARS

Course Objectives

At the end of this class, the student will be able to:

• Recognize different types of towbars and distinguish between different manufacturer’s towbars

• Describe operational checks and preventative maintenance for aircraft towbars

• Describe operation of basic components such as locking levers and hydraulic pumps

Course Objectives

At the end of this class, the student will be able to:

• Perform troubleshooting, disassembly, and reassembly

• Identify and install correct shear pins

Aircraft towbars are generally manufactured from round tubular steel or aluminum.

They have an “eye” or lunette, on one end to allow the towbar to be attached to the tow tractor.

The tow head, on the opposite end, allows the towbar to be attached to the aircraft tow point.

In the middle of the towbar is the undercarriage assembly. This is a set of wheels that can be lowered hydraulically to support the tow bar while it is being towed, or positioned at the aircraft.

You may find some towbars equipped with a rub strip under one or both ends of the body tube to protect it from abrasion.

Body Tube Accessories

You may see rub strips with extra feet welded to them.

Most tubes have handles bolted or welded to either end to aid the operator in positioning the towbar.

This handle is made from flat stock.

The flat stock handle is being replaced with a more comfortable round stock handle on newer towbars.

LUNETTES

The towing “eye” that is engaged by the tractor tow pin is called a lunette. It may also be called a hook-up bracket in some drawings.

Some lunettes may be welded to the bracket, and the entire assembly is bolted into the towbar body tube.

Some lunettes are attached to the mounting weldment with a large nut. On older towbars, these lunettes can be rotated.

However, on later model Clyde towbars, there may be a restrictor (arrow) welded to the flange above the lunette to prevent the lunette from rotating.

And some lunettes are simply welded onto the end of the towbar tube.

On some towbars, like this Zwicky model for the BAe 146 aircraft, the lunette is installed with special shear bolts.

On the older Wollard TB-561 towbar for the 747, the lunette threads on to a tension bar that runs through the middle of the body tube to the tow head.

The lunette on this PF Industries towbar is attached to the flange with a large nut. The nut is secured in place with a roll pin.

The PF Industries lunette and attachment.

The Clyde towbars use a similar arrangement. Here you see the lunette, the front flange, the washer, nut, and roll pin in their relative positions.

When assembled, the nut is inside the tube, and is only accessible when the front flange is removed.

On the Clyde TB-2672 towbar for the RJ-85 and Bae-146, the lunette weldment is attached with a single shear bolt.