MAP integrity check

[Echo_Kilo]

Hi,

ive seen that some airlines are performing a map integrity check prior to comencing their descent. How does this check work?

Cheers,

[Cough]

Dial up a vor/dme.

Compare radial/distance from the raw data with an FMC generated position via the fix page (Boeing) or the PROG page (Airbus). If result is > 2nm the position is unreliable, inhibit GPWS (if it doesn't have independent GPS) and fly the aircraft using raw data.