St. George, Utah based carrier SkyWest has been censured by the Federal Aviation Administration over a flying incident in April, imposing speed and altitude restrictions on its flights.
On April 23 a SkyWest Bombardier CRJ700 plunged abruptly 39,000 feet to 27,000 feet, which the US aviation regulator said was due to the pilot stalling at high altitude.
The FAA said SkyWest regional jets should fly no higher than 35,000 feet and must maintain minimum speeds.
"The FAA took this action following an event in which preliminary information indicates a SkyWest crew stalled an aircraft at cruising altitude," the FAA said.
Stalled aircraft have been attributed to many air crashes and can happen more easily at higher altitudes.
SkyWest, which operates regional services for United, Delta Air Lines Inc. and American Airlines, disputes the findings.
The decision was called a "sweeping and arbitrary reaction that was not fully explained and we believe is not supported by facts," said SkyWest spokeswoman Marissa Snow.
Snow said the aircraft did not stall and fell only 4,000 feet because of "less than optimal speeds."
Crew responded appropriately, Snow said.
SkyWest was handed two fines totalling more than $1 million earlier this week for two unrelated safety inspections.
