The National Transportation Safety Board issued Tuesday its final report on the investigation into the 2002 plane crash that killed Sen. Paul Wellstone (D-Minn.), blaming the fatal accident on pilot error and citing significant shortcomings in some of the charter operator’s crew training programs.

At the same time, NTSB members adopted a new set of safety recommendations for the unscheduled charter industry — also known as Part 135 “on demand” operators or air taxis. Such carriers are a popular method of travel among campaigning lawmakers like Wellstone, who was trekking around Minnesota just two weeks before Election Day when he was killed.

“It’s very important that out of tragedy good can come,” NTSB Chairwoman Ellen Engleman said at the outset of Tuesday’s hearing.

With the aid of charts, graphs and recordings of the final communications between Wellstone’s pilots and the control tower, investigators painted a vivid picture of what they believe happened to Wellstone’s twin-engine plane, which crashed on approach to Eveleth Airport in Minnesota on Oct. 25, 2002, killing all eight people aboard.

According to the NTSB, the “probable cause” of the crash — which claimed the lives of Wellstone, his wife, Sheila, daughter Marcia, three campaign aides, the pilot and co-pilot — was the “crew’s failure to maintain adequate air speed, which led to an aerodynamic stall from which they did not recover.”

Investigators said that NTSB accident databases revealed that since 1982, 18 commercial accidents have been caused by low airspeed.

As they described in painstaking detail the speed, altitude and location of Wellstone’s plane on its final approach, the investigators said there was absolutely no evidence of any sort of equipment failure or that any adverse weather conditions had contributed to the accident. They also ruled out pilot fatigue as a cause of the crash.

Frank Hilldrup, the lead NTSB investigator on the case, testified at the hearing that the probe had revealed “shortcomings in the proficiency of both pilots,” who were employed by Aviation Charter Inc. and that the company’s training was “inadequate” — potential explanations as to why the pilots had decreased the plane’s speed from 190 miles per hour to 87 mph in the final minute and a half of the flight.

“Evidence suggests that the flight crew made several errors during the approach,” testified Bill Bramble, a human performance investigator who worked on the case.

The key error, he said, was allowing air speed to “decrease to a dangerously low level,” which he said indicated that neither pilot was sufficiently monitoring the air speed or properly applying “Crew Resource Management” techniques, methods for facilitating proper decision-making, situation awareness and error management in the cockpit.

Bramble further testified that his investigation turned up inadequacies in Aviation Charter’s CRM training — and that post-accident interviews showed that CRM was not being properly taught at Aviation Charter.

Investigators also testified that Aviation Charter has not properly apprised its pilots of standard operating procedures, which if followed would have ensured the pilots had not been flying so close to stall speed, or that under the conditions they had encountered upon approach, they would have executed a “go around,” or reattempt their approach and landing.

“Interviews with the pilots [at Aviation Charter] indicate the pilots were not adequately aware of the company’s SOPs,” testified an NTSB investigator. “One pilot stated that she hoped the company would adopt a set of SOPs. Another said she used SOPs from a previous place of employment.”

In August, Aviation Charter agreed to pay the families of Wellstone and the aides who were killed a $25 million settlement. The company’s lawyer said the settlement was not an admission of any sort of wrongdoing or an acknowledgement of pilot error.

Among the safety recommendations adopted by NTSB members are “end route” inspections of Part 135, on-demand carriers, as is already done for other commercial carriers including major airlines and smaller commuters. These inspections would also include the observation of ground training and flight training methods employed by the carrier.

Moreover, the NTSB recommended required on-demand charter companies to conduct CRM training programs for two-pilot crews.

The NTSB also voted to convene a panel to determine if the installation of a low air speed warning system is a feasible addition to require in commercial aircrafts.

“The NTSB’s focus is on the determination of probable cause, as well as making safety recommendations,” Engleman said. “We will continue to aggressively pursue, as this accident report indicates, everyone in the safety chain. Everyone in the safety loop is responsible for safety.”