MOC 2 VTOL.2300 Acceptability of ASTM standard F3232/F3232M-20 for Fly-by-Wire flight control systems

1.      Status and comments

The ASTM F3232/F3232M-20 standard is the Standard Specification for Flight Controls in Small Aircraft. As this standard was prepared with the assumption of traditional (i.e. mechanical) primary flight controls, it can only be accepted as a means of compliance with VTOL.2300 for Fly-by-Wire (FbW) control systems with some explanations (see below), adaptations and additions (see Section 2) .

The definitions provided in §3 of ASTM F3232/F3232M-20 are only applicable insofar as the concept exists for VTOL capable aircraft and has not been defined otherwise. For instance: “aircraft type code” is not a valid concept for VTOL and “Continued Safe Flight and Landing” has been specifically defined for VTOL capable aircraft in MOC VTOL.2000.

Similarly, any reference in ASTM F3232/F3232M-20 to standards or methods for the determination of Handling Qualities should be considered to be replaced by a reference to MOC VTOL.2135.

Lastly, while this standard addresses conventional architecture elements such as flaps and stall barrier systems, different considerations may apply for other architectures in VTOL capable aircraft.

The following table provides the status of the acceptability of the ASTM F3232/F3232M-20 standard as a means of compliance with VTOL.2300 for Fly-by-Wire (FbW) control systems. Later revisions of ASTM F3232/F3232M or alternative standards may also be proposed by the applicant and agreed with the Agency as acceptable means of compliance in a particular certification project.

2.      Adaptations/additions to ASTM standard F3232/F3232M-20 linked to Fly-by-Wire implementation

(a)      Operation tests

To be considered an accepted means of compliance with VTOL.2300(a)(1) and (2), paragraph §4.7 of ASTM standard F3232/F3232M-20 should be adapted and complemented as follows:

(1)     Adaptation of ASTM F3232/F3232M-20 standard

4.7 Operation Tests:

4.7.1 It must be shown by operation tests that, when the controls are operated from the pilot compartment with the system loaded to the maximum actuation system forces (i.e. loads and torques), the system is free from jamming, excessive friction, excessive deflection, or any combination thereof.

NOTES:

(i)      It is acceptable to reduce the load slightly to enable movement of the actuator throughout its range.

(ii)     This requirement applies to primary and secondary flight controls that move surfaces and flight controls that move or redirect lift/thrust units. It does not apply to fixed propulsion units that vary RPM, blade angle, or thrust for flight control.

(2)     Addition to ASTM F3232/F3232M-20 standard

One method, but not the only one, for demonstrating the Operational Tests is as follows:

Conduct the control system operational tests by operating the controls from the pilot's compartment with the entire system loaded so as to correspond to the limit control forces established by the regulations for the control system being tested. The following conditions should be met:

(i)      Under limit load, check each control surface/effector for travel and detail parts for deflection. This may be accomplished as follows:

(A)     Support the control surface/effector being tested while positioned at the neutral position.

(B)     Load the surface using loads corresponding to the limit control forces established in the SC VTOL.

(C)     Load the pilot's control until the control surface is just off the support.

(D)     Determine the available travel which is the amount of movement of the surface/effector from neutral when the control is moved to the system stop. It is acceptable to reduce the load slightly to enable movement of the actuator throughout its range.

(E)      The above procedure should be repeated in the opposite direction.

(F)      The minimum control surface/effector travel from the neutral position in each direction being measured should be 10 percent of the control surface travel measured with no load on the surface.

Regardless of the amount of travel of the surface when under limit load, the aircraft should have adequate flight characteristics as specified in Subpart B. Any derivative aircraft of a previous type certificated aircraft need not exceed the control surface travel of the original aircraft; however, the flight characteristics should be flight tested to ensure compliance.

(ii)     Under limit load, no signs of jamming or of any permanent set of any connection, bracket, attachment, etc. may be present.

(iii)     Friction should be minimised so that the limit control forces and torques specified by the regulations may be met.