NTSB Factual Report

On November 25, 2007, at 0042 mountain standard time, a Boeing 737-832, N3744F, registered to and operated by Delta Air Lines, Inc., of Atlanta Georgia, and operating as flight 430, sustained minor damage when the tread on the right outboard tire came off and struck the airplane during takeoff from Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona. Visual meteorological conditions prevailed at the time of the incident. The flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 121, and an instrument flight rules (IFR) flight plan had been filed. The airline transport certificated captain and first officer, four flight attendants, and 160 passengers on board the airplane were not injured. The scheduled domestic passenger flight was originating at the time of the incident, and was en route to John F. Kennedy International Airport (JFK), New York, New York.

According to the crew's statements, as the airplane accelerated to 100 knots during takeoff, the ANTISKID INOP light illuminated. The takeoff was continued and no other anomalies were noted. Soon after leveling off at FL330, the crew was advised by air traffic control that tire fragments had been found on the runway and that they had possibly had a tire failure on takeoff. Shortly thereafter, the crew noticed hydraulic system A was losing fluid. The decision was made for the airplane to divert to Denver International Airport (DEN), Denver, Colorado. After declaring an emergency, the crew made an overweight landing on runway 16R using 40 degrees of flaps. The airplane landed at 0247. The crew allowed the airplane to roll almost the full length of the runway and stopped on a taxiway. The airplane was then towed to the gate.

Post-incident inspection revealed the tread on the right outboard tire had come off and had struck the inboard and midspan flaps, necessitating their replacement. In addition, the leading edge of the right horizontal stabilizer had been struck and required replacement. The tire was removed and sent to Goodyear for examination and analysis. According to Goodyear's report, "the most likely cause of the tread separation is [severe] overdeflection [underinflation and/or overloading) during use in service]."

On December 18, 2007, the same airplane, N3744F, was involved in another similar event. Departing JFK at 1946 and en route to PHX, the tread from the right outboard tire separated. According to Delta, damage was minor and was confined to the number 3 main wheel brake and wheel assembly. A small dent in the inboard trailing edge aft flap, approximately 21 inches from the inboard edge, was within the allowable damage limits. The pushrod for the panel over the gear and three cable fairleads were also damaged.

NTSB Probable Cause

Delamination of the right outboard tire tread during the takeoff roll due to underinflation and/or overloading during use in service.