MIL-STD-1901A
critical or directly influence safety critical functions to determine their contribution to the safety failure rate.
4.3 Ignition System. In order to preclude unintended or premature ignition system arming or initiation the ignition system shall:
a. Inhibit the arming sequence except as a consequence of a valid launch or confirmation of the launch intent.
b. Not be susceptible to common-mode failures.
c. Not contain any single point failure mode prior to or at the initiation of the arming cycle.
d. Delay arming as long as possible within operational constraints.
e. Utilize environmental forces, wherever possible, to enable safety features. When the IS utilizes stored energy to enable the safety feature(s), the stored energy source shall not be integral to the IS unless it can be demonstrated that it is impractical to do otherwise and that the required safety failure rate (see 4.5) can be achieved.
4.3.1 Ignition safety device. As an element of the ignition system, the ignition safety device shall:
a. Prevent arming or initiation of the propulsion system except in response to valid arming and launching signals from the ignition system.
b. Not contain any single point or common mode failure that could result in inadvertent or premature arming or firing prior to or at the initiation of the arming sequence
c. Delay arming as long as possible within operational constraints.
d. Utilize environmental forces, whenever possible, to enable safety features. When the ISD uses stored energy to enable the safety feature(s), the stored energy source shall not be integral to the ISD unless it can be demonstrated that it is impractical to do otherwise and that the required safety failure rate (see 4.5) can be achieved. In addition, if the ISD uses stored energy to enable safety features, it shall be as unique, in terms of
level and type, as allowed by system requirements.
4.4 Manual Arming. The ignition safety device shall not be capable of being armed manually unless such capability is required by operational conditions and is specifically approved by the responsible reviewing activity of 4.14. Such systems shall be capable of being easily returned to a non-armed condition under the conditions of deployment.
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