Airlines and their pilots have voiced concern over legislation that would allow gun-carrying guards on flights.
The Aviation Security Legislation Bill provides for tougher security measures, including the prospect of armed guards being allowed to fire guns on planes.
Airline Pilots Association representative Paul Lyons said pilots preferred tighter passenger screening and other ground-based security measures ahead of armed guards.
The association's technical officer Johnny Walker told Parliament's transport and industrial select committee, which is considering the bill, that firing a gun on a plane could easily cause it to crash.
"Serious consideration needs to be put into thinking about what happens if we have a missile or a projectile in the cockpit," he said.
"There are so many things it could hit that would actually disband that aircraft."
Vital aircraft equipment was held in the ceiling, floor and walls, which could be easily damaged by a bullet or a high voltage taser.
"How're you going to control that it's very difficult."
Transport Safety Minister Harry Duynhoven has said the provision is to allow armed air marshals to be deployed if another country, such as the United States, requires them.
Both airlines and their pilots today acknowledged the legislation was necessary so New Zealand flights were not barred from entering other countries, but said safeguards on air marshals were vital.
Mr Lyons said if another country required air marshals, the association would accept them -- so flights were not barred -- but only if there was extensive training and strict policies, developed in consultation with pilots.
Pilots would not support foreign air marshals on New Zealand flights, he said.
Board of Airlines New Zealand spokesman Stewart Milne said airlines were also nervous about the prospect of armed guards on flights, but they accepted guards might be necessary if another country made them mandatory.
If New Zealand put guards on flights it was vital they were properly trained, he said.
Mr Milne also raised concerns about increased powers of seizure in the bill.
Airlines were unhappy with wording which would require prohibited liquids to be seized and stored for 30 days, with the names of owners recorded -- similar to the regime for potential weapons.
Currently liquids are disposed of immediately.
At Auckland airport 2000 items are confiscated a day. Storing that and recording the names of owners would require about four more staff. It could also lead to possible flight delays, he said.
Airlines believed the power to seize and hold liquids should be discretionary.
The bill would also:
* allow the screening and searching of airport workers
* give aviation security officers the power to search passengers' outer garments and do pat-down searches
* require airlines to bar passengers who refuse to be searched
* allow aviation security officers to seize potential weapons.