Kiwi 52, an A4 Skyhawk, on a missed approach from a runway 35 ILS approach, had been issued with missed approach instructions to maintain runway heading and maintain 6000 feet. When Kiwi 52 was about four miles north of the aerodrome, the aircraft was instructed to turn right heading 070 degrees and to climb to and maintain 6500 feet. The altitude restriction was to maintain separation with VH-PZL, overflying at 7500 feet. As Kiwi 52 approached VH-PZL, Kiwi 52s altitude readout reached 7400 feet. When asked to confirm his level, the pilot of Kiwi 52 reported maintaining 6500 feet. Kiwi 52 was passed traffic information on VH-PZL. Shortly afterwards Kiwi 52s altitude readout returned to 6500 feet. The two aircraft closed to about two miles radar separation with Kiwi 52 passing behind VH-PZL. Factors The following factors were considered relevant to the development of the incident: The pilot of Kiwi 52 failed to follow an air traffic control instruction to maintain an altitude.