secondary glide slope
Capturing a secondary glide slope can lead
to unexpected aircraft behavior. It is important for the flight crew to be aware of
the phenomenon and to know how to prevent secondary glide slope capture.
When intercepting the glide slope from above, the flight crew should ensure that the aircraft is below the upper boundary of the main glide slope before they arm the approach. This boundary is located at approximately twice the value of the primary glide slope angle (approximately -6°).
This ensures that the capture will be done
on the correct glide slope. As a rule of thumb, a quick altitude vs. distance
check can be done to ensure that the aircraft is below the upper boundary of
the main glide slope.
The aircraft altitude above the airport
elevation (in ft) should be less than 6 times the distance to the runway (in NM)
multiplied by 100