Air safety investigators have started sifting through the remains of this morning's fatal plane crash in Sydney's south-west.

Police say the pilot made a call reporting engine problems just before his twin-engine plane hit power lines outside a house and school at Canley Vale.

The pilot of the aeromedical aircraft, 28-year-old Andrew Wilson, had reported difficulty maintaining altitude.

He and a flight nurse in her 40s were killed when the light plane crashed near the Canley Vale primary school.

Federal Transport and Infrastructure Minister Anthony Albanese says investigations have already begun into the cause of the crash.

"There has been a tragic loss of life. We know this has been a very tragic incident," he said.

"It's appropriate that the facts surrounding this incident be fully investigated and the Australian Transport Safety Bureau (ATSB) will be doing that."

Martin Dolan, the chief commissioner of the ATSB, says five investigators are heading to the crash site.

"They will examine the wreckage, they will interview witnesses and they will form an initial assessment of the facts and do a report on that and then move on to a more extensive analysis and investigation," he said.

"As you can imagine these things normally take some time. Normal standard for something of this kind is we will do a preliminary report within 30 days and expect to have completed all our work within a year.

"It's a twin engine aircraft and engine problems are rare and events of this nature a very rare."

The ATSB is appealing for any witnesses to the crash to contact it.

Mr Wilson had been flying for Wingaway Air for about four years.

The company's general manager, Steve Donoghue, says it has been a huge loss to the company.

"It's very sombre because when you're working with a group of eight or nine people who you work with daily, it's like losing a family member," he said.

"It's very difficult to cope."

Last conversation

Audio has emerged from LiveATC.net of the conversation between the pilot and the Bankstown air traffic control.

"We seem to be struggling with height a little; that's all mate," the pilot says to the control tower operator.

Mr Wilson then asks the tower operator if he can see the aircraft.

"At this stage negative due to haze," the operator responds.

"We're not maintaining height here. You got any sight? Are there any good roads around?" Mr Wilson asks.

"The M7 should be in your vicinity somewhere; you're just approaching the three-mile boundary now," the operator responds.

A tower does not have the authority to direct air traffic outside its three-mile boundary.

Mr Wilson says: "We've got no height here..."

"There's no main roadways in your vicinity?" the operator asks.

"We gonna have to put it down on the road," Mr Wilson responds.

The operator then says: "What about the raceway?"

"No, I can't see that, sorry," the pilot says.

Moments later the plane hit power lines before exploding.