MCP Altitude

[Sebastian Maguire]

Question:

Why are you not able to set the exact MCP altitude on a modern jet. Why only the FMC and VNAV if you want anything more accurate than the 100ft increments. Surely this would help in setting the accurate radio altitude targets etc.?

[BOAC]

SM - on a 737 at least, the radio altimeter minimum can be set very accurately for DH. Baro limits are set with a movable 'bug' on the altimeter which is not itself desperately accurate. We do not primarily use the MCP setting for minima for approaches (eg ILS) down to a radio minimum. During the 'procedure' up to the final approach the altitudes are always 'rounded-up' to the next 100ft and this does not cause a problem. The only advantage would be to be able to set MDA on a non-precision to the nearest 10ft, but the drudge of having to cycle though every 10 feet on the MCP window to change altitude every time...................

EDITIf this answer is not enough for you, let me know and I will move the thread to 'Questions'