(16)
 Fault Monitoring

 (a)  Fault monitoring consists of tests, checks and fault indications. The tests include Power-up Tests to check all input/output discretes, ram check, ARINC wrap-around and aural warning speaker check. Continuous tests include monitoring of all ARINC 429 inputs, source select of redundant ARINC inputs, monitoring discretes (level checks) and PROM checks. Confidence checks (CMC activated) are for takeoff warning and stall warning. Fault indications are messages displayed on the EICAS and CMC and fault annunciations on individual cards.

 (17)
 Aural Warning Sounds

 (a)  
Siren

 1)  The characteristics of the siren sound are two square wave signals F1 and F2 which are alternately switched on and off to produce a continuous output at a constant amplitude. F1 is 250 |50 Hz and F2 is 950 |100 Hz. The frequencies are switched every 0.5 |0.05 seconds.

 (b)  
Caution Aural

 1)  The characteristics of this sound are four consecutive identical tone bursts of constant amplitude each lasting for 160 |30 ms plus a quiet period of 45 |10 ms between tone burst.
 2)  Each tone burst consists of a frequency sweep which starts at 20 |5 Hz and linearly increases to 1000 |50 Hz in 50 |10 ms, and then remains at 1000 Hz for the remainder of the tone burst period.
 (c)  Fire bell
 1)  The characteristics of the fire bell sound are two constant frequency signals with exponentially decaying amplitudes summed with equal amplitude weighting.
 2)  The amplitudes of these signals are permitted to decay to 10 |5% of the original amplitude value and then are re-established to the original starting amplitude when the cycle is repeated. The amplitude of both signal components are re-established synchronously.
 3)  The two frequency values used are 1 KHz |0.1 KHz and 2 KHz |0.1 KHz. The time constant is 33 |2 seconds.
 (d)  Chime No. 1 1) Single stroke sound produced from a constant frequency and a decaying amplitude. The frequency is 580 |50 Hz.
 2)  The amplitude decay is symmetric with respect to the midpoint of the peak to peak signal of the 580 Hz tone. The decay time constant for the amplitude is 3.3 |0.2 seconds.
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747-400 MAINTENANCE MANUAL
 3)  The sound is terminated if the Chime No.1 input discrete is deactivated and is reinitialized if this input discrete is reactivated regardless of how much decay time has been used. Only one chime cycle is generated for each input activation.
Chime No. 2 (optional)
 1)  Dual stroke high-low chime is produced by generating a high frequency chime followed by a lower frequency chime. The frequency of the high chime is 1160 |50 Hz with a decay time constant of 3.3 |0.2 seconds off and an on time of 0.5 |0.1 seconds. The second or lower frequency chime is identical to Chime No. 1 and starts at the termination point of the high frequency chime.
Chime No. 3 (optional)
 1)  A single stroke sound produced in the same manner a Chime No. 1 except the frequency 1320 |50 Hz and it has a decay time constant of 4.5 |0.2 seconds.
Wailer (optional)
 1)  A single square wave, constant amplitude, signal increasing linearly in frequency from 125 |25 Hz to 325 |25 Hz. The period of repetition is 400 |25 ms.
Clacker (optional)
 1) The characteristics of the clacker sound are as follows: a) A single square wave, constant amplitude, constant frequency, signal broadcast as short interruptable tone bursts. b) The frequency of the signal is 2.0 |.1 KHz. The tone bursts last for 5 |.5 ms. c) Two tone bursts, spaced with a 20 |2 ms of dead time, are issued during each period. A period is 200 |25 ms.
Decision Height (DH) (optional)
 1)  Program pin option used to generate a height related variable audio sound starting fifty feet above the DH point and silencing at the DH point. Two versions of a DH aural are provided. These versions are selectable through the program pin option method.
 2)  Information used to generate DH data is determined by the crew alerting module and transmitted to the ASC on ARINC input port IAP1. Label 273, bits 17 through 11 provide information regarding the arming of the DH aural as well as the distance below the DH +50 foot initialization point.
　
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