MIL-STD-411F
A time delay, sufficient to allow the the landing gear to fully extend, shall be installed in the
wheels warning system to eliminate the nuisance activation and flashing of the "WHEELS" legend
indicator.
5.1.3.7 Wheels warning legend (VTOL aircraft). A "WHEELS" legend indicator, when specified by the acquiring activity (see 6.3.1), shall be installed on VTOL aircraft equipped with retractable landing gear. The indicator shall be connected so that it flashes whenever the airspeed and collective pitch (or other combination of functions approved by the acquiring activity, (see
6.3.1), indicate that the VTOL is configured for landing and the landing gear are not down and locked. A time delay, sufficient to allow the landing gear to be fully extended, shall be installed in the wheels warning system to eliminate the nuisance activation and flashing of the "WHEELS" legend indicator.
5.1.4 Caution signals. When required, legend caution and master caution signals shall be used in all aircrew stations. The master caution signal shall be energized simultaneously with any individual caution signal.
5.1.4.1 Color. Except where NVIS compatibility is required, the color of the caution signals shall be aviation yellow. Where NVIS compatibility is required, the color of the caution signals shall be in accordance with MIL-L-85762.
5.1.4.2 Legend. When illuminated, the legend shall be translucent on an opaque background as shown on figure 1. The character height of the legend shall subtend a viewing angle of not
less than 20 minutes of arc when measured from the aft most point of the design eye line (see
3.7). Character proportions shall be in accordance with MIL-M-18012. The minimum horizontal
separation between two legends shall be two times the width of the widest character. The
minimum vertical separation between two legends shall be two character heights. The minimum
vertical separation between two lines in the same legend shall be one-half the height of a
character.
5.1.4.3 Luminance. The luminance of the light signals shall be not less than 150 fL when the signals are operated at rated voltage at the point of entry of the light source. No less than two lamps, operating in parallel, shall be employed for each incandescent and light emitting diode type legend caution light. When installed in the flight aircrew station, the master caution signal shall be dimmed to 15 ± 3 fL and the caution signals shall be automatically reduced to 1.0 ± 0.50 fL when the pilot's primary interior light control is "ON". Caution signals shall be capable of being dimmed to a luminance of 0.1 fL when NVIS compatibility is required. The design shall preclude inadvertent dimming during daylight conditions. When installed in other aircrew stations, the caution signals shall automatically be dimmed to 15 ± 3 fL when the operator's primary panel light control is "ON". Except when NVIS are being used within a crew station, the dimmed caution signals shall be automatically reset to full bright when any of the following conditions exist:
a. Main aircraft power is turned off. b. Pilot's primary light control is off. c. High intensity lights are energized.
When an NVIS compatible lighting mode is being used within a crew station, the lighting circuit logic shall preclude the system from obtaining a luminance level which will degrade external vision or NVIS performance.
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