Investigators look through debris of a UPS cargo plane after it crashed in Birmingham, Ala., on Aug. 14, 2013. The two pilots aboard the airplane were killed. (Hal Yeager/AP)

The National Transportation Safety Board on Monday kicked United Parcel Service and its pilots union out of the investigation into the deadly crash of one of the delivery service’s cargo planes last summer.

The NTSB, in a sharp rebuke to the package delivery service, threw UPS and the Independent Pilots Association out of its ongoing probe for making public statements about the cause of the accident before the investigation was complete. Two pilots were killed in the Aug. 14, 2013, crash in Birmingham, Ala. No one else was aboard the plane.

“Statements in the UPS online comments impermissibly prejudge the results of the NTSB’s continuing investigation of the accident and its forthcoming findings and probable cause statement regarding the accident,” NTSB General Counsel David K. Tochen wrote to Mark McCloud, acting president of UPS’s airlines division. “The NTSB is hereby removing UPS’s party status in this investigation.”

Based on preliminary evidence from the crash, it is safe to assume that one aspect of the NTSB investigation focuses on whether the two pilots were too tired to be flying. When the pilots union raised the issue on the Air Cargo World blog earlier this month, a UPS public relations manager responded the next day.

“We have spent the past year working with the NTSB to determine what caused the accident and how to avoid such an accident in the future,” wrote Mike Mangeot, a spokesman for UPS Air Group in Louisville. “NTSB factual reports showed that the pilots’ schedules, as flown, would have complied with new FAA crew rest regulations for passenger carriers, even if they had been in effect and applicable.”

Mangeot responded Monday to his company’s ouster from the investigation, saying UPS had complied with the rules and wanted the NTSB to reconsider.

“We maintain that our actions have been in line with NTSB rules for communicating during an accident investigation,” Mangeot said in a statement. “We believe we have been unfairly reprimanded for attempting to set the facts straight and defending our brand.”

Understanding the gravity of the contretemps requires a glimpse into the fastidious fashion in which the NTSB does its job. In the case of an airplane crash, the NTSB calls in all the “parties” to the incident. For example, that might include the airline, the company that built the plane, the company that made the plane’s engines, various unions and any manufacturer who made a relevant system aboard the plane.

All take a vow of silence until the NTSB delivers its final report on the accident. So secret is the process that for some portions of the inquest the partners gather in a secure section of the NTSB building that is equipped with a unique computer system that allows no communication outside the room. Partners at those sessions take notes on color-coded paper that is collected before they leave the room.

In the August 2013 crash, Flight 1354 had departed from Louisville for the short flight to Birmingham-Shuttlesworth International Airport.

Just short of the Birmingham runway, the plane clipped some trees and struck the ground three times before a final crash at 4:47 a.m. and burst into flames.

The NTSB analysis of the cockpit voice recorder and flight data recorder two days after the crash found that the crew received two warnings 16 seconds before they crashed, indicating they were descending too quickly. But three seconds after that, one of the pilots was heard saying that the runway was in sight. About four seconds after that, the sound of an impact was heard on the voice recorder.

At a Feb. 20 NTSB hearing, voice recorder excerpts were presented in which the pilot, Capt. Cerea Beal Jr., 58,and co-pilot Shanda Fanning, 37, discussed that they were fatigued before beginning the flight.

Fanning told Beal that she had just gotten a “good sleep,” but she was still “so tired.”

The issue of rest time for pilots between flights has been controversial for several years. Pilot fatigue was seen as a significant cause of the 2009 crash of a Colgan Air flight bound for Buffalo, in which 49 people on board and a person in a house the plane crashed into were killed.

The NTSB found the accident was caused by the pilots’ inability to respond properly to the stall warnings.

Concern that pilots get sufficient rest led the Federal Aviation Administration to enact new rest rules in January for all pilots of commercial passenger planes. Cargo pilots felt they should be covered by the same requirements.

In the UPS flight cockpit conversation, Beal said, “This is where, ah, the passenger side (passenger airline pilots) . . . they’re gonna make out,” he said.

“I mean, I don’t get that. You know, it should be one level of safety for everybody,” he said.

Fanning concurred.

“It should be across the board to be honest. In my opinion, whether you are flying passengers or cargo or, you know, box of chocolates at night, if you’re flying this time of day . . . ,” she said.

Beal replied: “I know,” adding that cargo companies “got a lot of nerve.”

Tossing a partner out of an ongoing investigation is rare, but it happens. In December, the NTSB bounced a New York rail union from partnership in the investigation of a derailment that killed four people in the Bronx. In 2010, American Airlines was removed from an investigation into a plane that slid off the runway in Jackson Hole, Wyo. In 2009, the National Air Traffic Controllers Association was banished from an investigation into the collision of two aircraft over the Hudson River that killed nine people.

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