The US National Transportation Safety Board (NTSB) says air traffic controllers should have alerted pilots of an American Eagle ERJ-145LR of an embedded thunderstorm in their path at 38,000ft during a 28 June 2010 flight between Greensboro, North Carolina and Dallas Fort-Worth.
A flight attendant and one passenger received "severe" injuries when the aircraft experienced a strong updraft followed by a severe downdraft when the aircraft flew through the cell.
In its final report on the incident, issued 17 November, NTSB blames an "inadvertent encounter with convective weather during cruise flight" as the probable cause. Contributing factors were the flight crew's "failure to detect and avoid the thunderstorm cell earlier in the flight, and the failure of air traffic controllers to provide the convective weather information to the flight crew," the NTSB says.
After the encounter, the pilots declared an emergency and performed an emergency landing at the East Texas regional airport in Longview, Texas. The "fasten seat belt sign" had been turned on in tandem with an announcement by the crew about 10 minutes before the upset.
Both the captain and first officer told investigators they did not have time to decide on evasive action before penetrating the embedded cell, with the captain saying he first noticed the "very small red return" on the radar when it was 5nm (30 seconds) ahead of the aircraft. Based on what he saw when zooming in and tilting the radar controls, the captain had assumed the ERJ would fly over the top of the cell.
"Shortly after, they encountered rain and the strong downdraft, which threw them up into their seatbelts," the report states. "The captain stated that if he saw the cell at least 5 minutes beforehand he would have asked for a deviation since American Eagle's policy was to avoid cells by 20 miles."
Following the event, the airline reported that the pilots had lost the primary flight display (PFD) and multi-function display (MFD) on the first officer's panel and had noticed an electrical smell in the cockpit. "The airplane was examined and only a few burnt out bulbs were noted in the avionics panel," says the NTSB, noting that no structural damage had been found and that the aircraft was later returned to service.
After reviewing air traffic control data, investigators learned that a "moderate to severe" weather depiction ahead of the aircraft should have been visible on controllers' displays for "an extended period" before the upset, but that there had been no discussions of the embedded thunderstorm with the pilots, as is required by FAA operations orders.
"A review of recorded weather data from two separate air traffic control centers handling the flight showed that moderate to extreme intensity precipitation existed ahead of the airplane for an extended period," says the NTSB.
Investigators also found from weather surveillance radar (WSR) imagery a discrete cell of "strong reflectivity values coincident with the airplane's position" at the time of the turbulence encounter.
Controllers, in interviews, said they did not recall "seeing any displayed precipitation in the accident location, although they did recall seeing precipitation in other locations around the area", the NTSB notes.
"Review of display settings in use by the controllers showed no reason that the weather would not have been displayed," says the NTSB, "and there was no indication of a system malfunction."
Source: Air Transport Intelligence news
