Story ID: 
Citation’s Erroneous Altitude Data Led to Near-collision
By: Gordon Gilbert
Caption: French BEA says incorrect altitude information from a faulty air data computer in a Cessna CitationJet resulted in a near-collision with an Embraer 170.
Word Count: 495
Incorrect altitude information from a faulty air data computer in a Cessna CitationJet resulted in a near-midair collision with an Embraer 170, according to the final incident report incident from France's BEA. Because of the Citation's errant data, the Embraer's traffic collision avoidance system (TCAS) failed to warn of the close call, while the air traffic controller believed that the altitude separation was adequate based on radar data.
On Jan. 12, 2022, the French-registered Citation was carrying two pilots and two passengers on a charter flight from Paris to Geneva. After observing that the left and right altimeters were giving different indications on climb-out, the crew didn’t inform ATC of the discrepancy until they were en route. Controllers informed the Citation crew of converging traffic—the Embraer 170—two miles distant and 1,000 feet higher than the business jet. 
In reality, the EMB-170 was at a distance of 1.5 miles and 665 feet lower than the Citation. “No collision avoidance system warning, whether it be on the ground or onboard the Embraer 170, was emitted as the systems had analyzed erroneous data from the Cessna,” the report says. “Subsequently, the controller asked the [Citation] crew to deactivate their Mode C, and the flight continued” without further incident.
Investigation revealed that the fault on the Citation’s air data system 1 (altimeter and airspeed indicator on captain’s side) had occurred three other times on this airplane—in 2017, 2019, and 2021. Investigators believe that all four events could be traced to a low point in the pitot system hosing where water or other contaminants caused an obstruction.
After further investigation, which led to the removal and replacement of the pitot tube of system 1 and the hose eliminating the low point, the airplane was returned to service in early March 2022. To date, no fault of the air data system has been reported again. Textron Aviation said it is “not aware of any similar events in its fleet.”
Factors listed in the final report as contributing to the cause of the incident included: the crew’s failure to notify ATC immediately of the altitude anomaly, the controller not giving clear information to the crew concerning the altitude information available to him on his screen in response to questions from the crew, and the absence of a manufacturer and/or charter operator crew procedure to deal with cases of faults or uncertainties with respect to air data system indications.
The final report concludes with responses from Textron Aviation and the charter company to more than a dozen recommendations made during the course of the 18-month investigation.