Preventative Maintenance and Repair of Eagle Tugs
Tugs and Tractors in the aviation industry are called pushback vehicles, operated to maneuver an aircraft from its parking position, usually from an airport gate. IATA defines aircraft pushback operation as “rearward moving of an aircraft from a parking position to a taxi position using specialized ground support equipment.” Pushback operation is often considered a critical airport procedure carried out by Tugs and Tractors, unique low-profile vehicles to facilitate aircraft movement in the taxiways.
Tugs – Operation Procedure:
The operation is called Push “back” because the Tug driver does the steering, not by the aircraft pilot, since the pilot cannot see what is behind the aircraft. A Towing mechanism with a bypass pin is installed into the nose gear to disconnect it from the aircraft’s standard steering mechanism to connect tug to the plane. Once the pushback operation is completed, the towbar is disconnected, and any bypass pin is removed, following which the aircraft can taxi forward under its power.
Selection and Types of Pushback Tugs:
Aircraft tugs are classified into several types. However, for the selection of tug, the following classifications can be considered:
Classification based on Towing capacity:
Towing capacity is the tugs’ ability to pull or push a certain aircraft weight and is primarily dependent on the amount of traction generated by the tug. Eagle, a market leader in manufacturing GSE (ground support equipment), supplies tugs of different tow capacities as described below:
- Eagle TT Series: Towing capacity of 40,000 Kgs, traction of 8,000 lbf, and ideal for towing Challenger 850 and Citation Longitude aircraft.
- Eagle TT Series (High capacity): Towing capacity of 60,000 Kgs, traction of 12,000 lbf, and ideal for towing G550 and Global 6000 aircrafts
- Eagle XM Series: Towing capacity of 97,500 kgs, traction of 16,000 lbf, and ideal for towing B737 and A320 in all weather conditions
- Eagle XL Series: Towing capacity of 1,60,000 kgs, traction of 26,000 lbf, and ideal for towing B757 aircraft.
Classification based on drive source:
Small and lightweight airplanes are maneuvered by the ground staff using the aircraft’s nose or tail wheel. However, for heavier commercial and military aircraft, external power drives are necessary. Most commercial tugs are powered by IC (internal combustion) engines or electric/battery-powered mechanisms. Few tugs also operate on gas-powered mechanisms.
- Electric Powered Tugs: Eagle manufactures and supplies 80V AC electric aircraft tractors with a towing capacity of 70,000 kgs at 12,000 lbf traction, optimal for towing business aircraft such as G650 & Global 7000 in all weather conditions. The Eagle ETT tugs are known for low cost-per-hour of operation and zero hazardous emissions.
- IC Engine powered Tugs: Driven by a four-stroke, four or three-cylinder diesel engines, IC Powered tugs and tractors are popular amongst aircraft operators, primarily due to operational ease for taxing a wide range of aircraft. However, IC engines use high sulfur diesel fuel, which emits hazardous combustion particles to the atmosphere, causing air pollution and low visibility during winter and monsoon climatic conditions.
Conventional and Towbarless Tugs:
- Conventional tugs use a tow bar to connect the tug to the nose landing gear of the aircraft. Each aircraft type has a unique tow fitting, so the towbar also acts as an adapter between the standard-sized tow pin on the tug and the type-specific fitting on the aircraft’s landing gear. The tow bar can be connected at the front or the rear of the tractor, depending on whether the aircraft will be pushed or pulled.
- Towbarless (TBL) tugs do not use a towbar; they scoop up the nose landing gear and lift it off the ground. This avoids the time penalty of connecting/disconnecting a towbar and entirely removes the cost/complexity of maintaining towbars on the ramp. TBL tugs are very useful while operating a wide variety of aircraft in more confined spaces.
Preventative Maintenance of Aircraft Tugs:
Preventative maintenance (PM) is a proactive technique that follows a defined maintenance routine to assess all the tug and tow components before their breakdown, avoiding downtime losses and unexpected repairs.
Tug maintenance schedule includes repair and inspection of the following components:
| Sr.No | TUG COMPONENT | PARTS TO INSPECT | MAINTENANCE ACTIVITY |
| 1 | Engine Housing | Cylinder block and head | Inspection for wear and surface crack |
| 2 | Engine Gas distribution system | Air intake, inlet valves, Exhaust systems, exhaust valves | Inspection of Valve timings and piston rings |
| 3 | Shafts | Engine crankshaft and camshafts | Vibration readings (linear or torsional) as per ISO 10816 |
| 4 | Lubrication and cooling systems | Lube oil filter, oil quality, pump, and sump | Inspection of lube oil pressure for every use. Lab oil analysis at 50 running hours, pump vibration analysis, oil sump accumulation, and filter inspection at every oil change interval |
| 5 | Lubrication and cooling systems | Water jackets and pumps | Vibration analysis of pump and leakages or contamination of oil or coolant |
| 6 | Electrical system | ECU, Sensors, Actuating mechanism, and alternator | Functioning of DC components, alternator, emergency lights. Sensors (MPU Speed sensors), governor actuation, and alternator slip |
| 7 | Transmission and Differential | Gearbox, Clutch, and Differential gears | Inspection of gearbox vibration levels, gear teeth wear, clutch efficiency, and differential gear damages |
| 8 | Wheels and Brakes | Tires, axle, and brakes | Tire pressure, damage, axle bolts, brake actuation, and efficiency check |
| 9 | Steering and Chassis | Steering wheel, connection with axle, chassis, and suspension | Inspection of steering angle at full load, tug suspension, and connection lag with axle |
| 10 | Hydraulic systems | Plunger, oil pressure and level, leakages, and valves | Inspection of oil level, pressure leakages due to hose damage |
In addition to tug components, towing and tow bar mechanism PM (preventative maintenance) shall also be carried out as described below:
- Shear pins Inspection: These act as the prime load bearers while towing the aircraft, and operation should ensure that the pin stress does not exceed design PSI Limits—inspection of surface cracks, indentations, or crookedness due to excess load.
- Towbar body Inspection: Visual inspection must be carried for signs of the bent body, cracks, and dents. In case of abnormality, the towbar should be repaired and welded.
- Lifting mechanism: The primary function of a towbar is to raise the head to the required level above ground level. Until it is successfully connected to the vehicle, even the towbar wheels experience an upthrust. Therefore, the manual pump should be checked for pressure and proper fuel levels. Any cracks or leaks should be duly maintained to ensure pressure standards.
In addition to the PM inspections mentioned above, operational checks should also be followed daily as the OEM (Eagle) recommended.
Advantages of Preventative Maintenance Program – Why is it essential:
Although establishing and adhering to a PM program requires stringent control measures, they often prove beneficial for the aircraft operator in the long run. Following are few direct and indirect benefits of the Tug PM program:
- According to GSE standard guidelines, establishing a quality PM plan is mandatory for tugs
- Maintenance plan improves reliability & productivity of the tugs
- Proactive maintenance increases the machine availability and allows for optimal equipment operation
- PM ensures safety of personnel
- Savings in downtime losses and breakdown losses
e2b calibration offers industry-leading consultancy and certified PM services for your aircraft tugs. Our labs are ISO/IEC accredited and operated by a team of qualified experts providing training and consultancy services on Tugs maintenance and inspection. Our verifiable services are unmatched in the industry. Contact e2b calibration for all your equipment calibration needs.