A few bunches of flowers have been laid on the grass where four people died in a horrific light aircraft crash on Friday

Now it's just another paddock, like dozens of others in this nondescript little corner of Gundaroo.

But this one bears a sad and awful legacy.

A well-worn set of tracks have flattened the grass which leads down from the cattle grid to a small dam off Brooks Creek Lane.

There's an appropriate, respectful hush to the area. Aside from the birds in the nearby pines, there's just the faint rumble of trucks rolling up and down the Federal Highway.

Dozens of cars - at first police, ambulance, rural fire trucks, then more recently, air crash investigators - have flattened the tracks over days of activity, back and forth.

Several bunches of flowers are laid out on the grass just below the small dam where around 3pm on Friday, a US-built Cirrus single-engined light aircraft inexplicably plunged to the ground around 12 minutes after taking off from Canberra Airport.

There are no messages with the flowers. Because as a family friend noted in a GoFundMe page raised for the family "there are no words".

Four people died in the horrific impact. The 21-year-old aircraft had been piloted by Steve Nally, 65, from Bunyah in Queensland. He was an experienced pilot with hundreds of flight hours recorded.

His passengers were his three grandchildren: Raphael, 11, Evita, 9, and six-year-old Philomena Smith.

Random parts of the aircraft - a tailplane, a section of a door, two surprisingly intact propellors and sections of the engine - are still littered around the site, surrounded by a burnt patch of grass. The larger fuselage sections, which were evident shortly after the crash, have been taken away for investigation.

The Gundaroo crash site is so compact that it's difficult to process what occurred that day.

Experienced light aircraft pilots like Bywong local Alex Colquitt, who has flown an SR22, was equally confounded by what happened.

From his Macs Reef Rd property below the plane's flightpath, Mr Colquitt thought he heard a plane engine splutter overhead before 3pm Friday, but nothing untoward after that.

The Queensland-based Cirrus, like most aircraft, carried an ADSB system (Automatic Dependent Surveillance Broadcast) system which via a digital link shows position and altitude every half second.

Air traffic controllers from the Canberra tower had cleared the flight after take-off to "resume navigation and track direct to Culin". This is an air navigation waypoint situated north-east of Cullerin, near Goulburn.

Flight radar tracking data reveals the aircraft reached a height of 3000m at 2.48pm. Canberra air traffic control then advised it had dropped off their radar.

And as is often the case given the complexity of these investigations, it could be months before the Air Transport Safety Bureau hands down its initial findings.

The Cirrus aircraft company started fitting a safety device called CAPS (Cirrus Airframe Safety System) in the early 1990s, after the company's co-founder Alan Klapmeier survived a mid-air collision.

CAPS is a ballistic parachute which deploys from a receptacle in the roof of the aircraft via a handle in the roof. Externally it is attached at various points around the airframe. Once the parachute deploys, it is designed to suspend the airframe and bring it to earth.

Why the CAPS system was not deployed in the Gundaroo incident is part of the investigation.

The Cirrus Owners and Pilots Association reported there had been 145 CAPS deployments up to July 13 this year, of which 120 had been listed as "saves".