Eu queria postar isso como um comentário, mas é um pouco longo.
Da Convenção de Chicago da ICAO anexo 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.
...
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:
...
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.
Os padrões operacionais do equipamento de recepção do trajeto deslizante estão detalhados em RTCA DO-192 e EUROCAE ED-47B
Observe que o receptor só pode sentir uma diferença na profundidade de modulação (DDM), no sinal composto, não a profundidade absoluta de modulação de cada tom de áudio em cada radiador individual / acionado do arranjo faseado (o DM absoluto varia para cada indivíduo radiador / acionado - Exemplo ).
