Easy Street
All this TCAS stuff is long after my time, so a genuine question - one that arose during the Mull of Kintyre debate.
'Descend' instructions are inhibited below 1000 feet as measured on the radar altimeter
Taken literally, that could mean you have a rock face 1000' in front of you, with your huff and puff altimeter saying, say, 3000'. In other words, most Radar Altimeters measure the RANGE to the nearest fixed object within the beam pattern. The word "altimeter" can be misleading. So, for example, when the Chinook hit the hill at (800'?), the RadAlt indicated zero, or as near as dammit. Have I got this wrong? I remember this on MoK because the various reports seemed at times to confuse barometric with radar. (I've deliberately not mentioned Radio Altimeters!) Thanks.