Angel Flight West Executive Director Josh Olson confirmed on Wednesday morning that Spencer was flying the aircraft.
"Angel Flight West is devastated and deeply saddened to share that we lost one of our volunteer pilot Angels yesterday," Olson said. "Our thoughts and prayers are with the families of everyone on board."
Olson said the nonprofit has donated 75,000 flights to passengers in need since its founding 35 years ago.
"This is the first accident occurring with an Angel Flight West passenger on board," he added.
Both passengers were in stable condition and hospitalized, Stanford Health Care spokeswoman Lisa Kim said on Tuesday.
Anthony Dellamaria, a Redding resident, confirmed on Tuesday that his wife, Nancy Dellamaria, 49, and stepdaughter, Chloe King, 16, were on the aircraft. They were flying to Palo Alto so that Chloe could have surgery at Lucile Packard Children's Hospital, he said.
"Nancy has broken ribs and a fractured neck. I haven't been able to talk to her yet. Chloe is wearing a cervical collar and is under observation," he said from his home.
His wife's mother flew in Tuesday. She had planned to arrive for Chloe's scheduled surgery, he said.
"It's just sad," he added of Spencer's death.
Spencer had aborted an initial landing at the airport and was attempting to regain altitude around 11 a.m. when the crash into the marshland occurred, according to the Palo Alto Airport air-traffic control recording.
Minutes earlier, the tower operator and Spencer discussed landing the Mooney M20J aircraft. Spencer was coming in on a flight path near the Dumbarton Bridge. The tower operator cleared the Mooney for landing. Less than a minute later, Spencer said he was having trouble locating the field. The operator said Spencer would see it in the 11 o'clock position in about 2 1/2 miles.
About 40 seconds later, after trying to land the plane, Spencer said, "I'm going to have to abort this and go around."
The operator replied: "Make left. Close traffic. Do you need any assistance?"
"Negative," Spencer said calmly. "I just came in too fast."
Less than 50 seconds later, the operator issued an announcement: "Attention all aircraft. Due to a mishap we'll be shutting down pattern work and limiting operations in the vicinity."
Chris Ray, a fueler with Rossi Aircraft, which operates out of the municipal airport, said he saw the white plane approach the airstrip and bounce once on the tarmac before attempting a "go-around" maneuver. It looked to be going too low and slow to take off, however, and may have stalled, he told the Weekly.
Ray didn't see the crash, but he heard it and immediately went out in a truck with others to try to help. On the way, they picked up a nurse who had tried to wade out to the plane to render aid. She was unable to reach the aircraft because the mud was too thick, he said.
Upon arriving at the plane, which was in the Baylands northwest of the Palo Alto Duck Pond, they found Chloe in the back seat and Nancy Dellamaria injured in the front seat, he said. Spencer, who was in the mangled cockpit, was dead, he was told.
Emergency responders used a 24-foot extension ladder as a bridge to gain access to the plane.
One passenger was able to walk to the ambulance and the other was placed on a gurney, Palo Alto Fire Department Deputy Fire Chief Geo Blackshire said.
The plane was coming in from Redding, Blackshire confirmed.
Spencer, the registered owner of the plane, had volunteered as a pilot for Angel Flight West since 2014. He had served more than 75 families with 125 flights to help them receive the care they needed.
The nonprofit named him No. 2 Pilot of the Year in southern California in 2015 for flying 47 missions. (Rankings were based on the number of missions flown.) He was named Pilot of the Year again in 2016 for flying 32 missions as wingman.
Everyone associated with the nonprofit was trying to get over the shock of the incident, Olson said Tuesday.
Carin Powers, an Angel Flight volunteer who had been waiting to pick up King and Dellamaria in her car, said they didn't have a scheduled time of arrival, which was a bit unusual.
"It was a last-minute signup to pick them up. I called the pilot and the mother and asked them to let me know when they would be coming in. I never heard from them until about 15 minutes before they landed. Nancy texted that they were about to land at the airport in 15 to 20 minutes. She told me not to worry. They would be happy to wait at the airport," Powers said by phone on Tuesday evening.
Powers said she texted back that she couldn't arrive at the airport until about 11:45 a.m.
"I didn't hear back. I tried to call her and I couldn't reach her. I just decided to go there. Just when I got there, I saw the fire engines and the news trucks, and I knew something had happened," she said.
Powers said she ran into another Angel Flight pilot, Orhan Baser, who confirmed the plane's tail number, and she then knew the incident involved the mother and daughter she had come to meet. She said she did not know the pilot.
"I've been doing this for a little over a year. The pilots are so awesome. It's so sad. It's a wonderful organization in all that they do," she said.
Powers added that she knows many people don't like the Palo Alto Airport and that its existence has been controversial. (In the past, some residents have called for the airport's closure, claiming it is hazardous, creates noise and serves an elite few.)
"But that airport is extremely vital for these patients," she said.
Baser had been in the air when the crash occurred below. The winds had shifted at the time of the incident, he said, but he didn't know if that played a role in the crash.
An average of 525 planes take off, land or execute other flight operations at the airport per day, according to AirNav.com, based on FAA information for the 12 months ending May 22, 2018.
On Tuesday, nine departures and 17 arrivals had taken place prior to the crash.
Andrew Swanson, Palo Alto Municipal Airport manager, said Tuesday evening that he and Operations Manager James Wadleigh immediately went to the scene and had been there all day. The city will work closely with National Transportation Safety Board (NTSB) staff, who will lead the investigation, he said.
"It's just a tragic accident. The investigation is a lengthy process. (NTSB) will tear the engine down to try to figure out what went wrong. They don't speculate, although it's human nature to do so," he said.
Out of concern that plane fuel may spill into the slough, city of Palo Alto staff is consulting with the U.S. Department of Fish and Wildlife as well as other federal agencies prior to removing the plane from the slough, said Daren Anderson, the city's division manager for Open Space, Parks, and Golf. The work is legally required to be the least environmentally disruptive, he said.
Two engine companies, two ambulances and the fire department's battalion chief responded to the scene on Tuesday morning.
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