Flight Log aLTITUDES

Sometimes the altitudes in the flight log alt column show a strange variation. For example on descent, it may show 40,000, 36,000, 25,000, 12,000 showing a progressing descent, then an instant jump up to 30,000, followed by the rest of the descent profile. 8,000 for example, and maybe another spike to a higher alt before the descent resumes normally again. What causes this? Thanks. Tom

Essentially, ATC clears them to that ‘jump’ altitude at that point.

As state elsewhere in this forum, what happens is that ATC radar loses the altitude of the aircraft. It substitutes the filed altitude.

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Here is one such discussion

I always figured that the altitudes were actually mode C reported altitudes, not ATC cleared altitudes, and that strange deviations were a result of reporting errors…

Thanks for the help. Regards, tom