What Size Tug Do I Need: Pushback Tractor Capacity vs. Aircraft Pushback Resistance
Let me first begin by stating that I am no mathematician or physicist, in fact I am far from either…
However, I do receive many inquiries from customers who have a difficult time selecting the proper aircraft tug for their exact application. So for my first several posts I want to focus specifically on aircraft pushback tractors (and will provide more GSE info in the future).
Correctly matching your tug’s drawbar pull rating (DBP) to the aircraft’s maximum take-off weight (MTOW) will reduce pushback and towing incidents. The following information will serve as a good guide in providing the proper towing equipment for your ramp operations as it is a common subject in the aircraft handling world.
The International Air Transportation Association (IATA) in a Toronto meeting summary memorandum titled “Push back communications” stated that 87% of ramp accidents occur during aircraft push back. 82% of those accidents involve the nose gear.
The conclusions were:
- Better training of the pushback procedures to pushback personnel are required.
- Improved communications with the cockpit by the pushback tractor operator are required.
- Proper pushback tractor and towbar capacity for the size of aircraft being moved will result in elimination of towbar and nose gear damage.
IATA Airport Handling Ground Support Equipment Specification AHM 955: “Functional Specification for an Aircraft Tractor.”
Paragraph 1.4 states ”There shall be four categories of tractors defined in accordance with the maximum aircraft weight.”
- Category 1 – aircraft less than 50,000 kg. (110,000 lb.)
- Category 2 – aircraft less than 150,000 kg. (330,690 lb.)
- Category 3 – aircraft less than 260,000 kg. (573,196 lb.)
- Category 4 – aircraft more than 260,000 kg. (573,195 lb.)
Paragraph 3.7 states “The minimum tractor weight for each class as defined in paragraph 1.4 shall be”:
- Category 1 – 4,000 kg. (8,800 lb.)
- Category 2 – 12,000 kg. (26,455 lb.)
- Category 3 – 18,000 kg. (39,683 lb.)
- Category 4 – 40,000 kg. (88,184 lb.)
Category 2, 3 or 4 tractors, generating 300% to 1000% greater DBP when pushing Category 1 aircraft can greatly increase pushback issues caused by excessive power. Aircraft pushback incidents therefore increase because the towbar and nose gear are not rated to absorb the excessive power of these larger tugs.
The Category 1 tractor has pushback power protection limits as follows:
- Tractor’s drive wheel(s) will slip and lose traction when the Category 1 DBP traction weight (8,800 lb.) is exceeded.
- The torque converter will stall at 8,000 lb. DBP to protect the towbar and/or aircraft nose gear.
*These protections are not available when using Category 2, 3 or 4 tractors to push Category 1 aircraft.
Basically stated, using the correct tug for the weight of the aircraft you are moving is essential; as you may find yourself purchasing an aircraft nose gear that far exceeds the cost of a new tractor…
AERO Specialties is dedicated to providing equipment to safely handle your GSE requirements. To make things simpler we have compiled a list of the proper pushbacks for the majority of the aircraft in operation around the world. Don’t hesitate to ask if you require verification or advice.
Your comments are invited and greatly appreciated!