Note: This question is a little ambiguous, but feedback has confirmed that the answer is 245 ft

Height keeping errors that must be reported by the crew, investigated by the operator and then sent to the overseeing authority within 72 hours include those errors where the aircraft shows an altimetry system error of ± 245 ft.

Some useful numbers for the exam:

• Assigned altitude deviation of ±300 ft (±90m)
• Total vertical error of ±300 ft (±90m)
• Altimeter system error of ±245 ft (±75m)

EASA AIR OPS
Regulation (EU) No 965/2012
SPA.RVSM.115 RVSM height-keeping errors

(a) The operator shall report recorded or communicated occurrences of height-keeping errors caused by malfunction of aircraft equipment or of operational nature, equal to or greater than:

(1) a total vertical error (TVE) of ± 90 m (± 300 ft);
(2) an altimetry system error (ASE) of ± 75 m (± 245 ft); and
(3) an assigned altitude deviation (AAD) of ± 90 m (± 300 ft).

(b) Reports of such occurrences shall be sent to the competent authority within 72 hours. Reports shall include an initial analysis of causal factors and measures taken to prevent repeat occurrences.

(c) When height-keeping errors are recorded or received, the operator shall take immediate action to rectify the conditions that caused the errors and provide follow-up reports, if requested by the competent authority.