On climbout from Tindal, the crew heard a loud bang and the gear Unsafe light came on. Speed was reduced to 180 knots indicated air speed and the gear cycled. On Down selection, the two maingear lights were green but the nosegear indicated Unsafe. On selecting Up, the Unsafe light remained on. The flight was continued to Darwin below 180 knots. On arrival, two flights past the tower were made. On the first flight with gear selected Up the nosegear was reported to be in the normal extended position. On the second flypast with gear selected Down, only the two maingear lights were green and the tower reported that the gear appeared to be extended normally. Procedures for the emergency extension of the gear did not obtain a safe indication for the nosegear leg, and the pilot did not apply inflight loads to the aircraft in an attempt to lock the nosegear down. The pilot carried out a normal circuit and landing and held the nosewheel off the runway for as long as possible. At approximately 80 knots the nosewheel was lowered gently onto the runway but it collapsed almost immediately. The aircraft remained on the runway centreline as it slid to a halt on its nose. Subsequent specialist investigation showed that the nosegear actuator rod end had failed due to fatigue and stress corrosion.