Originally Posted by
pattern_is_full
This is not an inherent problem with the GS equipment at VHHH. It is due to departing aircraft on the ground proceeding into the ILS Critical Area and interfering with the GS signal.
Clearly well-known to the authorities, since they have carefully painted an ILS HOLD line on taxiway K, abeam the GS antenna (see top image, post #43, and the airport diagram). And not uncommon at other airports.
If the ceiling is below 800' and/or visibility is below 2 miles, and an aircraft is on the ILS inside the OM, ATC should not permit an aircraft (or other vehicles) to pass that hold line. because it is well-known that that can make the GS reception unreliable.
However, on this day, the weather was well above those requirements, and ATC was not required to protect the GS signal.
Therefore it is up to landing crews, well-informed by charts, NOTAMs, and ATC verbal warnings that the GS could be unreliable as departing aircraft interrupt it periodically in good weather, to use common sense and not be automation-dependent. Use the ILS for guidance if you wish, but be prepared for a honking great 747F to pass in front of the antenna and foul up the GS signal. Be ready to hit the VS HOLD button, or cancel the A/P altogether and hand-fly the rest of the approach manually and visually.
It’s OK then. Until an aircraft nosedives into the ground.
Then they will fix it.