Jag ville posta detta som en kommentar, men det är lite länge.
Från ICAO Chicago Convention bilaga 10, vol 1 :
2.3 Alarm conditions for ILS airborne equipment
2.3.1 Ideally, a receiver alarm system such as a visual flag should warn a pilot of any unacceptable malfunctioning conditions which might arise within either the ground or airborne equipments. The extent to which such an ideal may be satisfied is specified below.
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2.3.3 The alarm system should indicate to the pilot and to any other airborne system which may be utilizing the localizer and glide path data, the existence of any of the following conditions:
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b) the percentage modulation of either the 90 Hz or 150 Hz signal reduction to zero with the other maintained at its normal 20 per cent and 40 per cent modulation respectively for the localizer and glide path;
Note.— It is expected that the localizer alarm occur when either the 90 Hz or 150 Hz modulation is reduced to 10 per cent with the other maintained at its normal 20 per cent. It is expected that the glide path alarm occur when either the 90 Hz or 150 Hz modulation is reduced to 20 per cent with the other maintained at its normal 40 per cent.
Operationsstandarder för glidbanans mottagningsutrustning beskrivs i RTCA DO-192 och EUROCAE ED-47B
Observera att mottagaren endast kan känna av en skillnad i modulationsdjupet (DDM), i komposit-signalen är inte det absoluta djupet på moduleringen av varje ljudton vid varje enskild radiator / driven av fasstyrningen (absolut DM varierar för varje enskild individ radiator / driven - Exempel ).
