A sea plane pilot had to turn to avoid the bridge after failing to get enough height, but turned back under the bridge to avoid a boat (file photo).

A pilot has been fined $1500 after flying under the Auckland Harbour Bridge when he failed to gain enough height during takeoff.

Gerald Gwynn Chisum, 75, pleaded guilty at the Auckland District Court in 2019 for flying a plane in a careless manner.

Chisum was flying a seaplane carrying five passengers on a scenic flight over Rangitoto Island in December 2017, according to a recently released court decision.

The flight left Westhaven Marina just after 11am with Chisum piloting the plane out of Wynyard Wharf and around the headland, before turning left towards the Auckland Harbour Bridge.

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As Chisum prepared for take off near the bridge, he could not take off clear of the bridge due to a cross-wind and the type of plane he was flying, court documents said.

Judge Robert Ronayne noted it should have been clear to Chisum prior to take off that he risked getting too close to the bridge.

"Even if the defendant did not realise before commencing his take off, he should have realised soon after, and aborted take off before the bridge. Instead of aborting take off, the defendant continued.

"This action was careless."

Chisum turned right when he realised that he did not have enough power in the conditions and continued parallel to the bridge, the decision said.

After turning right, Chisum saw a stationary boat so turned left towards the bridge.

Chisum managed to pass "low and fast" under the bridge and continued his take off after passing under.

Ronayne reduced the fine due to Chisum's "long and trouble-free" flying career, as well as giving a discount for an early guilty plea.

Chisum was fined $1500, together with court costs of $130.

The pilot has been flying in New Zealand since 1994, and has over 40,000 hours of flying experience.

He was flying a seaplane for Auckland Seaplanes Limited at time time of the incident.

Auckland Seaplanes has been approached for comment.