AFGS�87219B APPENDIX A
REQUIREMENT GUIDANCE (A.3.2.3)
Consult with the cognizant subsystem engineers to determine if flight systems exist, whether uninterruptible power is required, and the degree of redundancy required. On aircraft with flight-critical subsystems requiring electrical power, the EPS also becomes flight-critical.
REQUIREMENT LESSONS LEARNED (A.3.2.3)
a. Experience has shown that an emergency power source intended for operation only after a malfunction has occurred is not a suitable backup for fly-by-wire flight controls. The startup and operating reliability of the emergency power units is deficient for this purpose. It is necessary to have full-time redundant power sources to meet the fly-by- wire requirements.
b. One aircraft started out with a mechanical flight control system with a fly-by-wire system as a backup. Part way through the design, the fly-by-wire became primary with the mechanical system only usable in certain portions of the flight envelope. This late change resulted in significant redesign of the electrical system to meet redundancy and uninterruptible power requirements.
c. Even though reliability analyses have shown aircraft EPS to exceed the requirements for flight-critical systems, total electrical power system failures have occurred on every aircraft. To prevent the loss of an aircraft, it is strongly recommended that a PMG be installed on each engine shaft to provide last-ditch power to keep the aircraft in the air.
A.4.2.3 Uninterruptible power.
Compliance with the requirement for uninterruptible power shall be verified by analyses and tests as follows: .
VERIFICATION RATIONALE (A.4.2.3)
Analyses and tests are the appropriate means of verifying the requirement for uninterruptible power.
VERIFICATION GUIDANCE (A.4.2.3)
a. Circuit analyses, hazard analyses, and failure mode and effect analyses are appropriate. b. Subsystem tests in the laboratory and on the aircraft should be required.
VERIFICATION LESSONS LEARNED (A.4.2.3)
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