AC 25.901-1
7.8.9.1.5 Alternatively, if in lieu of a flight deck alert the applicant relies on visual detection means to annunciate improperly latched nacelle cowl doors and other maintenance access doors during pre-flight inspection, the applicant should provide sufficient attention-getting characteristics and appropriate design features in order to reduce exposure to an unsafe system operating condition and validate the effectiveness of those means per the following:
1. Provide clearly visible detection means under all anticipated operating and environmental conditions that can occur during pre-flight inspection. Airplane features should not obscure visual detection means. A visual inspection should not require maintenance crew or flightcrew to lie on the ground or bend low.
2. Provide features that are easily distinguishable, such as bright ly colored markings. Other features could include a design that holds cowls, access doors, or latches open with a large visible gap between surfaces (for example, the cowls remain clearly open when not properly latched).
3. Evaluate detection at various distances and locations around the airplane.
4. Evaluate detection in anticipated environmental and operating conditions. The detection means should be effective at night and during adverse weather expected to occur within allowable airplane dispatch conditions.
5. Evaluate detection accounting for the flightcrew’s pre- flight walk-around inspection procedure for the airplane design.
7.8.9.2 Failure of cowling latches or other restraints may cause a significant displacement of a surface and result in drag that adversely affects airplane performance or significantly increases fuel consumption.
7.8.9.3 Failure of cowling seals, pressure relief doors, and other surfaces that allow hazardous drainage of flammable fluid, violation of fire containment integrity, or impede passenger egress during an engine fire.
7.8.9.4 Failure of the cowling “hold open” mechanisms that pose a hazard to maintenance personnel. See related guidance in paragraph 7.7 on personnel hazards.
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