No Sponsor,
The 6 degree false glideslope has indeed an opposite indication due to the 90hz. Lobe under the 150hz. Lobe. ( the intersecting line gives the glideslope as we know)
The 9 degree glideslope however IS correct in indication as the 150hz. Lobe is below the 90hz. Lobe.
In reality, most false glideslope incidents happen by catching the 6 degree slope. Where the Autopilot might indeed start a pitch-up manoeuvre.
On B747-400,When the AFDS senses a glideslope within the established criteria, it will capture. A thing that is not that well known by some Airlines crews however, is that if there is interference or loss of signal of the UHF glideslope signal, the AFDS will continue the remembered glidepath. This should happen only below 200ft. Agl though. Strangely enough, this is not mentioned in the Standard Boeing issued FCTM or OM of the -400.
It is almost impossible to understand why a crew is following a LVP without checking the G/S during the whole approach, being so high, not knowing what they were doing at all.
We all make mistakes, and we endeavour to learn from them, but this smells of a deeper problem within the Company Culture.
Last edited by Icelanta; 8th Feb 2017 at 20:12.