A security officer who planted a fake bomb at Dunedin Airport has had his sentence cut in half.

Preetam Prakash Maid, 33, was jailed for three years over the incident which happened just days after the Christchurch mosque shootings in 2019.

However, the Court of Appeal this afternoon released its judgement ruling the sentence was "manifestly excessive".

It imposed a substitute term of 17 months' imprisonment and allowed Maid the chance to apply for home detention.

It was a "somewhat unusual" case, Justices Matthew Muir, Denis Clifford and Susan Thomas said.

Curiously, the Court of Appeal found, the act of placing the laptop bag containing the imitation improvised explosive device beside a hut near the runway was not the crux of the criminal offence.

Maid was convicted of taking the item through a "security enhanced area" (SEA), an act which happened earlier, lasted three minutes and caused "no anxiety, alarm, or consequence of any kind".

The legislation, the court said, was designed to capture offenders who intended to smuggle explosive devices onto aircraft but were stopped before boarding.

"He had no intention of boarding an aircraft with the [device] or even placing it in the vicinity of one," said Justice Muir.

"His objective was not to cause terror to any one or more individuals. It was therefore in the nature of happenstance that an offence took place."

In reducing the penalty, the court took issue with the sentencing judge's assessment that the offending was near the most serious of its kind.

"We would reserve such description to transit through a SEA with a firearm or live explosive with the intention of subsequently boarding an aircraft," said Justice Muir.

Maid, the court heard at trial, had been vocal with superiors about what he perceived to be inadequate security in some areas of the airport and the Crown said the bomb hoax was his way of exposing those supposed shortcomings.

Despite the jury's guilty verdict, the former security officer has staunchly maintained his innocence.

Swipe-card analysis showed that on March 17, 2019, he twice entered a corridor to the dangerous goods store, spending 20 minutes there.

Maid took items from the storeroom — a SodaStream gas canister, a decommissioned cellphone, and red and black wiring — and stashed them in a laptop bag knowing it would resemble a bomb.

While conducting a perimeter check of the airport, he slipped the bag into the alcove of a "localiser hut" at the north end of the runway before sounding the alarm.

Once the item was neutralised by the New Zealand Defence Force, police picked through the remains and discovered the items inside had come from within the airport.

The most critical piece of evidence came from a cryptic handwritten note wrapped around the bag's handle.

"A: Alpha, B: Birds, C: Crash, D: Dunedin, E: Emergency, F: Fools," it said.

The court was shown a comparison of Maid's handwriting and the penmanship from the note, and a forensic document examiner said she was confident the defendant was the author.

The court rejected the appeal against conviction.

Because of the time he has already spent in prison, it is understood Maid will be released next month if he opts not to apply for home detention.