MOC VTOL.2305 Landing Gear Systems

1.      Scope and Definitions

(a)      This MOC applies to

(1)     Wheeled landing gear, not to a skid, ski or float design.

(2)     Tricycle landing gear arrangements of Nose and Main Landing Gears.

(3)     Ground control of the vehicle, for the landing gear, pertains to steering by turning any of the vehicle wheels.

(b)     The guidance assumes

(1)     Normal take-off and landing is vertical. Forward-speed landings might be made for non-normal (emergency) conditions.

(2)     No significant longitudinal engine thrust on ground

(3)     Steering system is restricted to low-speed taxi only

(4)     Ground resonance addressed separately, at aircraft-level

Note: Running take-off and landing (similar to fixed-wing aircraft) will be considered in a future update of this MOC.

2.      Interference with Extension/Retraction

It should be shown that, in any practical circumstances, movement of the pilot’s ground control (including movement during retraction or extension or after retraction of the landing gear) cannot interfere with the correct retraction or extension of the landing gear, unless it can be shown that such interference cannot create a consequence worse than Major, as defined in VTOL.2510.

3.      Towing

If it is intended to tow the vehicle via the landing gear (either via tow-bar or via direct attachment to the wheel(s)), the ground control system(s), towing attachment(s), and associated elements should be designed or protected by appropriate means such that during ground manoeuvring operations effected by means independent of the vehicle:

(a)      Damage affecting the safe operation of the ground control system is precluded, or

(b)     A flight crew alert is provided, before taxi commences, if damage may have occurred.

4.      Wheels

(a)      The wheel should be approved, to ETSO C26d or equivalent

(b)     The maximum static load rating of each wheel should not be less than the corresponding static ground reaction with:

(1)     Maximum weight; and

(2)     Critical centre of gravity.

(c)      The maximum limit load rating of each wheel should equal or exceed the maximum radial limit load determined under the applicable ground load requirements of this SC.

5.      Tyres

(a)      If the landing gear is fitted with a tyre, then it should be a tyre:

(1)     That is a proper fit on the rim of the wheel; and

(2)     Of a rating that is not exceeded under:

(i)      The design maximum weight;

(ii)     A load on each main wheel tyre equal to the static ground reaction corresponding to the critical centre of gravity; and

(iii)     A load on nose wheel tyres to be compared with the dynamic rating established for those tyres equal to the reaction obtained at the nose wheel, assuming that the mass of the vehicle acts at the most critical centre of gravity and exerts a force of 1.0 g downward and 0.25 g forward, the reactions being distributed to the nose and main wheels according to the principles of statics with the drag reaction at the ground applied only at wheels with brakes. Dynamic elements may be omitted for vehicles which usually take off and land vertically, and for which a running landing is Extremely Improbable.

(b)     Each tyre installed on a retractable landing gear system should, at the maximum size of the tyre type expected in service, have a clearance to surrounding structure and systems that is adequate to prevent contact between the tyre and any part of the structure or systems.

(c)      ETSO C62 provides the appropriate tyre performance standards. This ETSO accepts the use of a 1.5 factor on the Tyre Rating for helicopters. This factor is also appropriate to be used in VTOL vehicles which take off and land vertically (i.e. equivalent to helicopters).

6.      Brakes

(a)      The brakes should also be adequate to counter any normal unbalanced torque when starting engines or rotors.

(b)     A park brake should be included which will hold the vehicle stopped, on a 10 degree slope, on a dry and smooth runway, for whichever is most demanding of the following three cases. In each case a steady wind speed of at least 17 kt, or higher defined by the applicant, from the most adverse direction should be assumed in order:

(1)     To allow sufficient time for emergency egress and to secure the vehicle in place via other means

(2)     To counter any unbalanced torque when starting or stopping rotating lift/thrust units

(3)     To react any element of longitudinal thrust from lift/thrust units, albeit that the take-off and landing will be vertical.

(c)      The brakes should have adequate controllability and stopping capacity to bring the vehicle safely to a halt for any emergency running landing (including an immediate re-land). Such a running landing need not be considered if it arises from failure combinations determined to be Extremely Improbable, as defined in VTOL.2510. ETSO-C26c contains minimum performance standards for wheels and wheel-brake assemblies. The relevant rotorcraft section  of this ETSO may be used when following this MOC.

(d)     Any fatigue or endurance effect of applying the brake during high-speed taxi should be taken into consideration.

(e)     Means should be provided for each brake assembly to indicate when the heat sink is worn to the permissible limit. The means should be reliable and readily visible.

(f)      Compatibility of the wheel and brake assemblies with the vehicle and its systems should be substantiated.

7.      Landing Gear Warning

If a retractable landing gear is used, an aural or equally effective landing gear warning device should be provided that functions continuously when the vehicle is in a normal landing mode and the landing gear is not fully extended and locked. A manual shut-off capability should be provided for the warning device and the warning system should automatically reset when the vehicle is no longer in the landing mode.

8.      Landing Gear Position Indication

If a retractable landing gear is used, there should be a landing gear position indicator (as well as necessary switches to actuate the indicator) or other means to inform the pilot that each gear is secured in the extended (or retracted) position. If switches are used, they should be located and coupled to the landing gear mechanical system in a manner that prevents an erroneous indication of either “down and locked” if each gear is not in the fully extended position, or of “up and locked” if each landing gear is not in the fully retracted position.

9.      Landing Gear Emergency Extension

If a retractable landing gear is used, emergency means should be provided for extending the gear in the event of :

(a)      Any reasonably probable failure in the normal retraction system; or

(b)     The failure of any single source of hydraulic, electric, or equivalent energy.

10.     Operation Tests

The proper functioning of the extending/retracting mechanism must be shown by operation tests.

11.     Landing Gear Lock

There should be a positive means (other than the use of the LG extension power source) to keep the landing gear extended in the landing position.