U.S. accident investigators took the unusual step of removing United Parcel Service Inc. and its pilots’ union from a probe into the cargo-jet crash that killed two people last year in Birmingham, Alabama.

The company and the Independent Pilots Association “took actions prejudicial to the investigation” by issuing comments and analyzing findings before the National Transportation Safety Board meets to determine the cause, the agency said today in an e-mailed release.

NTSB includes manufacturers, airlines and unions as parties to investigations to provide technical assistance. While they are also allowed to lobby the agency on its findings, the safety board limits what they can say in public.

“If one party disseminates information about the accident, it may reflect that party’s bias,” NTSB acting Chairman Christopher Hart said in the release. “This puts the other parties at a disadvantage and makes them less willing to engage in the process, which can undercut the entire investigation.”

UPS and the Independent Pilots Association didn’t immediately return messages left for comment about the NTSB’s action.

The UPS plane, an Airbus A300-600F, crashed shortly before dawn Aug. 14 as it was preparing to land in Birmingham. It hit trees and a utility pole before slamming into a hillside and bursting into flames.

Captain Cerea Beal, 58, of Matthews, North Carolina, and First Officer Shanda Fanning, 37, of Lynchburg, Tennessee, died in the accident.

Documents and testimony at a Feb. 20 hearing showed the pilots made several errors as they attempted to touch down at Birmingham-Shuttlesworth International Airport’s Runway 18, which is 5,000 feet (1,524 meters) shorter than the alternate landing strip and lacked an instrument-landing system that guides aircraft on a constant descent.

The accident has raised questions about fatigue and pilot actions.