Investigators are set to brief lawmakers on the DC midair collision Thursday | Here's what we know

WASHINGTON -- Investigators trying to figure out what led to the deadly midair collision between a US military Black Hawk helicopter and an American Airlines plane near Washington, DC, last week will brief lawmakers Thursday on what they've learned after combing through data from both aircraft and air traffic control.

Officials from the National Transportation Safety Board and Federal Aviation Administration are expected to speak to the bipartisan group as the effort to pull wreckage from the cold waters of the Potomac River continues less than five miles away.

Here's what we know about the investigation into the crash that left 67 people dead:

Investigators analyzing data

The NTSB is grappling with conflicting altitude data as it works to piece together how the collision unfolded.

The agency said Tuesday the Potomac TRACON (Terminal Radar Approach Control) data for the Black Hawk, which was stationed at Fort Belvoir in Virginia and flying a training mission, showed it at 300 feet shortly before the collision. The helicopter's designated route had a strict altitude limit of 200 feet, according to FAA charts.

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Potomac TRACON is a regional air traffic control facility that fuses information from multiple radar sensors and the data each aircraft broadcasts on its position using GPS technology.

However, radar readings from the airport tower place the helicopter at 200 feet, while the commercial jet's flight data recorder reported an altitude of 325 feet, NTSB board member J. Todd Inman stated over the weekend.

The NTSB has said that a clearer understanding of the Black Hawk's position will only emerge once its wreckage is recovered from the Potomac River, which is expected to happen in the coming days. In the meantime, the FAA has indefinitely suspended the use of most designated helicopter routes over the Potomac.

Both the aircrafts' flight data and cockpit voice recorders - commonly known as black boxes - have been recovered. Investigators have been working to synchronize the recordings to better understand the events leading up to the collision. And separate teams continue to review maintenance records for both aircraft.

"Every piece of the information is critical to the investigation, and the NTSB is about transparency," NTSB board chair Jennifer Homendy told CNN's Pete Muntean on Monday.

Officials have cautioned against drawing premature conclusions into the cause of the crash.

Determining the Black Hawk's precise altitude at the time of the collision is seen as a crucial step in understanding how two aircraft collided under clear skies over some of the country's most tightly controlled airspace.

The NTSB is expected to release a preliminary report on the crash within 30 days. While final investigations often take more than a year to complete, Homendy voiced optimism that this case could progress more quickly.

"I would hope it would be much less than that," Homendy said.

What investigators are examining on the wreckage

Crews led by the NTSB and the US Navy Supervisor of Salvage and Diving have pulled significant pieces of the passenger jet from the Potomac River, including its right wing, sections of the fuselage, the cockpit and key flight systems, according to the NTSB.

The wreckage is being sent to a secure location "for a full wreckage layout and examination," the NTSB said.

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The investigation will include a detailed inspection of the jet's major components, structural damage, and fracture surfaces as well as an assessment of its overall "airworthiness," the NTSB said. Investigators will also examine cockpit switch positions and instrument readings, the agency said.

Crews working on the wreckage recovery face another day of cold and wet conditions Thursday. A winter weather advisory is in effect until 10 a.m. for icy conditions, before transitioning to rain later in the morning and clearing by the afternoon.

All 67 victims have been identified

All 67 victims have been recovered and identified, officials said Wednesday.

Among those victims was Ian Epstein, a charismatic American Airlines flight attendant who was remembered in a celebration of life In North Carolina Wednesday, CNN affiliate WBTV reported.

"He was just the greatest guy who made everybody happy all the time," Lynne Southmayd, a former flight attendant, told WBTV.

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