Glide Slope Scalloping
A good twist on the original thread SR71, GS scalloping can be severe in some instances. It should be remembered that the nominal surveyed area for Localiser is 25 NM, the surveyed area for GS is the same 25 NM longitudinally, but within Localiser coverage laterally. NOTAMs / Airways Manual notification may indicate lesser tolerance at various locations, and conversely, at some locations GS is airways tested and certified at lateral limits outside the Localiser coverage.
The worst case I've seen is at Phuket (VTSP / HKT) in Thailand RWY 27, where steady 'on Glide Slope' indications are common when tracking to intercept the localiser, but suddenly jump to 'full fly up' when established on the Localiser - Users BEWARE!
On the other side of the coin, it was once common to have ATC instruction in Singapore to "Descend on the Glide, call established on the Localiser". (I haven't heard this one for some time now, perhaps they don't include this larger area of GS coverage in the regular airways testing / calibration any more).