Latest On DC Mid-Air Collision

On Friday, February 14, 2025, National Transportation Safety Board (NTSB) Chairman Jennifer Homendy held an Investigative Update to the midair collision between PSA Airlines Bombardier CRJ700 and the Sikorsky UH-60 Blackhawk.

100-Foot Disparity Between the Blackhawk Pilot and Copilot’s Cockpit Altimeters

The NTSB reported there was a 100-foot disparity between the Blackhawk pilot and copilot’s cockpit altimeters. Since Blackhawk helicopters have both barometric pressure and radio altimeters installed, and the Chairman was not clear as to which she discussed, it is unknown which altimeter had the 100-foot disparity. However, the disparity likely happened with the helicopter’s barometric altimeter, as the Washington, D.C. helicopter route structure is described in feet "mean sea level” (MSL), and MSL altitudes are measured by the barometric altimeter, not the radio altimeter. Additionally, Sean Paine, Branch Chief of the NTSB’s Vehicle Recorder Division, noted that the Blackhawk’s radio altimeter was providing valid data at the time of the midair.

Pilots flying in controlled airspace maintain their assigned altitude using the aircraft's barometric altimeter. Barometric altimeters operate by measuring atmospheric pressure. As an aircraft climbs, the atmospheric pressure decreases. The altimeter senses this decrease in pressure and displays the decrease as a change in feet of altitude.

Atmospheric pressure also changes as an aircraft flies from one geographic area to another. To ensure aircraft in the same geographical area use the same barometric pressure setting, pilots are instructed by air traffic controllers to adjust their barometric altimeters to a “local” barometric pressure setting.

Entering the correct setting is critically important. If a pilot fails to adjust the barometric pressure setting, or if they set the wrong value, the aircraft could be off altitude by hundreds of feet. NTSB investigators will likely strive to determine whether both Blackhawk pilots had the correct local altimeter setting in their barometric altimeters at the time of the crash.

Additionally, the NTSB found that the “pressure altitude” recorded in the Flight Data Recorder (FDR) was invalid. What the NTSB intended by "invalid" is unclear, but pressure altitude calculated by modern air data computers (ADCs), like the one installed on the accident Blackhawk, is dependent on the barometric pressure setting that is entered by the pilot.

Moreover, the error allowed in barometric altimeters is surprisingly large. Barometric altimeters need only be accurate to plus or minus 75 feet, which is not much of a margin when helicopters and aircraft are operating with only a few hundred feet of vertical separation, as was the case in the airspace at the Washington-Reagan airport.

C.F.R §91.411 mandates all aircraft in controlled airspace that operate under Instrument Flight Rules (IFR) have the altimeter and altitude reporting equipment tested every two years, or after maintenance. Since U.S. military aircraft operate under Part 91, NTSB investigators will check if the U.S Army complied with §91.411, and whether the U.S. Army properly tested the Blackhawk's altimeter and altitude reporting equipment.  

Automatic Dependent Surveillance-Broadcast (ADS-B)

The NTSB reported that the UH-60 Blackhawk was equipped with Automatic Dependent Surveillance-Broadcast (ADS-B) “Out”, but that the Blackhawk was not transmitting ADS-B Out at the time of the midair collision.

ADS-B has two components, ADS-B “Out” and ADS-B “In”.

In 2020, the FAA mandated that all aircraft operating in U.S national airspace be equipped with ADS-B Out. When equipped, ADS-B Out transmits aircraft GPS position to air traffic controllers via the aircraft's transponder to ground control stations located throughout the United States.

ADS-B “In” is optional; however, it offers numerous advantages. Aircraft equipped with ADS-B In receive the ADS-B Out position data from other aircraft directly, as well as receive position data of aircraft not equipped with ADS-B Out via ADS-B ground control stations. This position data is displayed to a pilot on a cockpit monitor, and shows the range and bearing of those other aircraft. Pilots can also receive aural traffic alerts when other aircraft are in close proximity.

The NTSB is currently investigating the reason the Blackhawk was not transmitting ADS-B Out at the time of the midair collision. It is unknown at this time whether the Blackhawk pilots turned the system off, or whether there was an issue with the equipment installation, or an equipment malfunction.

Visibility Study

The National Transportation Safety Board (NTSB) plans to conduct a "visibility study" to determine if the pilots of the CRJ700 and UH-60 Blackhawk could have visually acquired each other from their respective cockpits as the aircraft converged.

The visibility study will involve laser scanning a CRJ700 cockpit and a UH-60 Blackhawk cockpit, as well as gather data on each pilot's height, seating position, eye position, and consider the impact of night vision goggles (NVGs) and their limited field of view (FOV).

This data will be input into a computer program to create a simulation depicting the pilots' field of view from the cockpit.

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