Boeing overwrote surveillance footage from the repair facility where a door plug was reinstalled ahead of the blowout on an Alaska Airlines flight earlier this year, according to a letter Wednesday from National Transportation Safety Board Chairman Jennifer Homendy to the Senate Commerce Committee.

The NTSB has been requesting the footage in order to investigate what happened during the midflight scare.

The NTSB still does not know which Boeing employees worked on the failed door plug of Alaska Airlines 1282, which had its door plug blow out during a flight in January, Homendy also said in the letter.

"To date, we still do not know who performed the work to open, reinstall, and close the door plug on the accident aircraft," Homendy wrote to Sens. Maria Cantwell and Ted Cruz. "Boeing has informed us that they are unable to find the records documenting this work."

Boeing did not immediately respond to a request for comment.

During her hearing in front of the committee earlier this month, Homendy informed lawmakers that Boeing had not yet handed over documents needed in their investigation, including the names of 25 people who worked on the door plug. Following the hearing, Boeing provided a list of names to the NTSB of personnel who reported to the door crew manager, but that list did not identify who performed the door plug work, according to Homendy.

Homendy stated in her letter that she then contacted Boeing CEO Dave Calhoun after receiving the list and asked for the names of those who performed the work. Calhoun "stated he was unable to provide that information and maintained that Boeing has no records of the work being performed," according to Homendy's letter.

"The absence of those records will complicate the NTSB's investigation moving forward," Homendy wrote in the letter, which was requested in response to questions during her testimony in front of the committee.

Homendy insisted in the letter that her agency is "not in any way seeking the names of employees who performed the work on the door plug for punitive purposes" -- saying she instructed the NTSB to protect the identities of the door crew and other front-line employees who come forward.