The fatal plane crash yesterday in Canterbury was witnessed by glider pilot John McCaw, uncle of All Blacks captain Richie McCaw.
Mr McCaw was at the glider club when the PA28236 Dakota aircraft crashed near Springfield, killing pilot Martin Lowen, 55.
He said he was "not in the headspace'' to talk about the crash today.
"I'm just sort of feeling the effects of today,'' he said.
"I'm quite upset about it. It's not something you'd want to witness.''
His wife Jill posted on her Facebook page that she had been speaking to her husband on the phone when he saw the plane crash.
"John was there and on the phone to me at the time. He and others raced through gorse and shrubbery to try and get to the site and help the pilot, to no avail - as the aircraft was exploding in flames.''
The McCaw family are heavily involved in gliding, and the couple's two sons are also pilots.
Richie McCaw has spoken about his family's long involvement with the sport, with his father and two uncles also flying gliders.
Fire melted the fuselage of the plane, slowing the work of safety investigators from the Civil Aviation Authority (CAA).
CAA spokesman Mike Richards said three investigators were at the scene, but it was too early to say what may have caused the accident.
"There are many many hours of painstaking work sifting through the ash from the wreckage to see if there are any clues that may explain what happened,'' Mr Richards said.
"Our investigators have found it particularly challenging as the fire from the impact has even melted the aluminium fuselage of the aircraft.''
The light plane had been towing a glider with two people on board, which was able to release from the tow and land safely.
Mr Richards said the engine of the plane was mostly intact, and was likely to be sent to a specialist firm in Dunedin to be stripped back to search for a mechanical cause of the accident.
"The team are now taking a detailed photographic record of the site and surrounding area and will also review police photographs and pictures taken by an off-duty TAIC investigator who was in the area yesterday.
"The next step will be interviewing eye-witnesses. The glider that was being towed by the Dakota PA28236 got away safely with both a pilot and instructor on board so they will be important witnesses to this tragic accident.''
Mr Richards said that due to the severe fire and the need for outside technical experts, it may be up to 12 months before the results of the investigation are known.
"However if the CAA identifies anything obvious that may have caused the accident it will alert the aviation community with the utmost urgency.
"Our goal is to learn what can from this accident and help prevent something similar happening again.''
The CAA said no update was yet available on the investigation into a second fatal aviation accident yesterday.
A glider crashed on a property near the Auckland Gliding Club airfield in Drury, South Auckland, killing the sole occupant on board.
The glider which crashed in Drury was seen by Bruce Owen, from Opaheke, who said it disconnected from the tow plane in an unusual place.
Mr Owen posted on Facebook: "We were having a cuppa just before 4.00pm outside on the deck. We were watching a glider being towed into position. It let go at an unusual place and turned back toward the Drury gliderdrome at a steep descent and at quite a fast speed.
"Diana remarked at the speed and wondered if something was wrong. Later we heard that there had been a crash not far from us.''
The CAA said an update will not be available on its investigation until tomorrow.
Police said the dead pilot had not been formally identified and the name was likely to be released tomorrow.
The glider came down on a neighbouring property to Franklin Local Board chairman Andy Baker's home.
Mr Baker said he didn't see the crash but saw the glider's shadow pass over. "My son saw the shadow and said `gee, that glider was close to the house','' he said.
He was alerted to the incident when phoned by a neighbour, and found police and ambulance officers already on the scene when he went to investigate.
Mr Baker said the crash was traumatic for the teenagers who were among the first on the scene.
"There were a lot of young kids around, a lot of teenagers around down there,'' he said.
"It was pretty traumatic for them.''