CS 25.509 Towing Loads — CS-25

IRImplementing rule

CS 25.509Towing Loads

(See AMC 25.509)

(a)The towing loads specified in sub-paragraph (d) of this paragraph must be considered separately. These loads must be applied at the towing fittings and must act parallel to the ground. In addition –

(1)A vertical load factor equal to 1·0 must be considered acting at the centre of gravity;

(2)The shock struts and tyres must be in their static positions; and

(3)With WT as the design ramp weight, the towing load, FTOW is –

(i)0.3 WT for WT less than 30 000 pounds;

(ii)for WT between 30 000 and 100 000 pounds; and

(iii)0·15 WT for WT over 100 000 pounds.

(b)For towing points not on the landing gear but near the plane of symmetry of the aeroplane, the drag and side tow load components specified for the auxiliary gear apply. For towing points located outboard of the main gear, the drag and side tow load components specified for the main gear apply. Where the specified angle of swivel cannot be reached, the maximum obtainable angle must be used.

(c)The towing loads specified in sub-paragraph (d) of this paragraph must be reacted as follows:

(1)The side component of the towing load at the main gear must be reacted by a side force at the static ground line of the wheel to which the load is applied.

(2)The towing loads at the auxiliary gear and the drag components of the towing loads at the main gear must be reacted as follows:

(i)A reaction with a maximum value equal to the vertical reaction must be applied at the axle of the wheel to which the load is applied. Enough aeroplane inertia to achieve equilibrium must be applied.

(ii)The loads must be reacted by aeroplane inertia.

(d)The prescribed towing loads are as specified in the following Table:

Tow Point	Position	Load
Tow Point	Position	Magnitude	No.	Direction
Main gear		0·75 FTOW per main gear unit	1 2 3 4	Forward, parallel to drag axis Forward, at 30° to drag axis Aft, parallel to drag axis Aft, at 30° to drag axis
Auxiliary gear	Swivelled forward	1·0 FTOW	5 6	Forward Aft
	Swivelled aft	1·0 FTOW	7 8	Forward Aft
	Swivelled 45° from forward	0·5 FTOW	9 10	Forward, in plane of wheel Aft, in plane of wheel
	Swivelled 45° from aft	0·5 FTOW	11 12	Forward, in plane of wheel Aft, in plane of wheel

[Amdt 25/13]

IR · CS 25.509 — CS-25 · ED Decision 2013/010/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

AMCAcceptable means of compliance

AMC 25.509Towbarless towing

Show the text

(a)General Towbarless towing vehicles are generally considered as ground equipment and are as such not subject to direct approval by the (aircraft) certifying agencies. However, these vehicles should be qualified in accordance with the applicable SAE ARP documents. It should be ensured that the nose landing gear and supporting structure is not being overloaded (by static and dynamic (including fatigue) loads) during towbarless towing operations with these vehicles. This should be ensured by the aircraft manufacturer, either by specific investigations as described in subparagraphs (b) and (c) below, or alternatively, by publishing aircraft load limitations in a towbarless towing vehicle assessment document, to allow towbarless towing vehicle manufacturers to demonstrate their vehicles will not overload the aircraft.

(b)Limit static load cases For the limit static load cases, the investigation may be conducted by rational analysis supported by test evidence. The investigation should take into account the influence on the towing loads of the tractive force of the towing vehicle including consideration of its weight and pavement roughness. Furthermore, the investigation should include, but may not be limited to, the following towbarless towing operation scenarios:

(1)Pushback towing: Moving a fully loaded aircraft (up to Maximum Ramp Weight (MRW)) from the parking position to the taxiway. Movement includes: pushback with turn, a stop, and short tow forward to align aircraft and nose wheels. Engines may or may not be operating. Aeroplane movement is similar to a conventional pushback operation with a towbar.

(2)Maintenance towing: The movement of an aeroplane for maintenance/remote parking purposes (e.g. from the gate to a maintenance hangar). Aircraft is typically unloaded with minimal fuel load.

(3)Dispatch (operational) towing: Towing a revenue aircraft (loaded with passengers, fuel, and cargo up to Maximum Ramp Weight (MRW) from the terminal gate/remote parking area to a location near the active runway. The movement may cover several kilometres with speeds according to SAE ARP 5283 technical standards, with several starts, stops, and turns. It replaces typical taxiing operations prior to take-off. Operations that are explicitly prohibited need not to be addressed.

(c)Fatigue evaluation Fatigue evaluation of the impact of towbarless towing on the airframe should be conducted under the provision of CS 25.571 and CS 25.1529. Specifically, the contribution of the towbarless towing operational loads to the fatigue load spectra for the nose landing gear and its support structure needs to be evaluated. The impact of the towbarless towing on the certified life limits of the landing gear and supporting structure needs to be determined. The fatigue spectra used in the evaluation should consist of typical service loads encountered during towbarless towing operations, which cover the loading scenarios noted above for static considerations. Furthermore, the spectra should be based on measured statistical data derived from simulated service operation or from applicable industry studies.

(d)Other considerations Specific combinations of towbarless towing vehicle(s) and aircraft that have been assessed as described above and have been found to be acceptable, along with any applicable towing instructions and/or limitations should be specified in the Instructions for Continued Airworthiness as described in Appendix H, paragraph H25.3(a)(4) and in the Aeroplane Flight Manual as specified in AMC 25.745(d). Aircraft braking, while the aircraft is under tow, may result in loads exceeding the aircraft’s design load and may result in structural damage and/or nose gear collapse. For these reasons, the aircraft manufacturer should ensure that the appropriate information is provided in the Aeroplane Maintenance Manual and in the Aeroplane Flight Manual to preclude aircraft braking during normal towbarless towing. Appropriate information should also be provided in the Instructions for Continued Airworthiness to inspect the affected structure should aircraft braking occur, for example in an emergency situation.

[Amdt 25/13]

AMC · AMC 25.509 — CS-25 · ED Decision 2013/010/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023