Air New Zealand has revealed that not one but two of its domestic flights had to make unscheduled landings on Sunday.
The airline says an oil leak caused NZ417 - a Boeing 737 with 101 people on board - to malfunction on a flight from Auckland to Wellington and make an unscheduled landing in Hamilton.
A passenger says he heard a huge bang and the plane rolled to the right and left before dipping. Another says that there was panic and that one passenger needed oxygen; others were in tears.
It has now emerged that flight NZ2144 from Gisborne to Auckland returned to Gisborne after what Air New Zealand calls a possible engineering issue.
A few minutes into the flight, the airline says, the pilots observed erroneous power readings from the port engine, so the captain shut it down as a precaution.
Air New Zealand says the 1900D Beech was inspected, tested and returned to service after the engine was found to be without fault.
The nine passengers were transferred to the next flight.
Authority to monitor investigation
The Civil Aviation Authority (CAA) will monitor Air New Zealand's investigation into both incidents, which the airline has reported to the authority, and determine whether the results are satisfactory and whether a CAA investigation is required.
For its part, the Transport Accident Investigation Commission (TAIC) says it is not investigating the incident on the Auckland-Wellington flight, because the engine failure was controlled - it was not something like an explosion that would have put the aircraft at risk.
Airline Pilots' Association Association technical director Stu Julian says professional pilots are well trained in engine failure and know how to land with just one working.
When an engine failure occurs, Captain Julian says, the procedure is to "aviate, navigate and communicate".
In the case of the aborted Auckland-Wellington flight, Air New Zealand says the pilot followed procedure and shut the malfunctioning engine down.
The airline says the engine will be taken to Auckland, where the source of the leak will be investigated.