A microburst likely was a major factor in the July 31 accident involving an Aeromexico Embraer E190 that went down as it was departing Durango, Mexico, with investigators reporting they have not found any mechanical anomalies or obvious errors made by the aircraft's pilots.

In a Sept. 5 update on the probe, Mexico's Directorate General of Civil Aeronautics (DGCA) said investigators found evidence of a microburst above the airfield as the aircraft, operating as Aeromexico Connect Flight 2431, prepared for its scheduled departure to Mexico City. A short-duration storm moved in as the aircraft was taxiing out, changing the airfield's conditions rapidly.

The three-person flight crew—which included a first officer in training who was sitting in the right seat and serving as the pilot flying—was not given any weather information that would have prompted them to consider delaying its departure, investigators said.

The factual information released by DGCA suggest the aircraft became unstable during or just after liftoff, with its left engine striking the runway's edge. The aircraft was airborne briefly before coming down and continuing just past the runway end. All 99 passengers and six crew onboard survived.

DGCA conducted simulator sessions with "several" crews using the conditions experienced by Flight 2431. In each case, the results were the same: an accident. This helped investigators conclude that the pilots did not make any mistakes during the departure, DGCA said.

Investigators found no mechanical issues with the aircraft's two General Electric CF34-10E engines, though further analysis of its FADEC system are being conducted. The No. 1 engine had 26,768 total hours, including 2,737 since its last overhaul. The No. 2 engine had 20.072 hours since new, and 14,614 since its last overhaul.

The aircraft's systems also showed no anomalies, DGCA said. The aircraft, serial no. 173 and carrying registration XA-GAL, was delivered in May 2008 to Republic Airlines, which was leasing it to Aeromexico. The aircraft had 27,257 total hours when the accident occurred.

Among the issues likely to be examined closely as the probe continues: whether the crew received adequate meteorological updates leading up to the departure, and if Aeromexico's flight-training procedures contributed to the accident.

DGCA expects to have its final report out by December.

Sean Broderick, sean.broderick@aviationweek.com