N332NW

HISTORY OF FLIGHTOn August 8, 2015, about 0202 coordinated universal time (all times in this report are in coordinated universal time unless otherwise noted), Delta Air Lines flight 1889, an Airbus A320-211, N332NW, penetrated a thunderstorm and encountered large hail while in cruise flight at flight level (FL) 340 over Max, Nebraska. The flight crew declared an emergency and diverted to Denver International Airport (DEN), Denver, Colorado. None of the 119 passengers, 2 pilots, and 3 flight attendants sustained injuries, and the airplane sustained minor damage. The flight was being operating as a 14 Code of Federal Regulations (CFR) Part 121 regularly scheduled passenger flight from General Edward Lawrence Logan International Airport (BOS), Boston, Massachusetts, to Salt Lake City International Airport (SLC), Salt Lake City, Utah. Night instrument meteorological conditions were reported along the route of flight at the time of the incident.

The flight was originally scheduled to depart BOS at 2130, but air traffic control (ATC) delayed the departure until 2225. According to a review of automatic communication and recording system (ACARS) data, at 2103, the assigned flight dispatcher, located at the Delta Air Lines Operations Control Center (OCC) in Atlanta, Georgia, generated a flight release and sent it to the flight crew. According to the dispatcher, it included an ATC-preferred routing to SLC because "there wasn't much weather enroute prior to getting out to the west." At 2106, the dispatcher sent the flight crew an initial weather briefing for the flight, which noted that there was a chance of afternoon thunderstorms around the destination airport. At 2150, he sent an updated weather briefing indicating that there had been "no weather updates since the previous transmission."

The airplane taxied from the gate in BOS at 2229 and departed at 2244. The climb to FL340 and initial cruise were uneventful. The first officer was the pilot flying (PF), and the captain was the pilot monitoring.

In post incident interviews, the captain reported that, as the flight progressed through Minneapolis Air Route Traffic Control Center (ZMP ARTCC) airspace, he and the first officer observed a line of thunderstorms ahead of the airplane on the weather radar. The captain added that he was operating the weather radar manually and using the "calibrated" mode to view the weather.

At 0129, the ZMP controller initially advised the flight crew about a large area of moderate-to-extreme precipitation on their current flight route in western Nebraska and noted that they would likely need to significantly deviate to get around it. The company dispatcher reported that he had also observed the weather and, at 0138, he sent a message to the flight crew via ACARS indicating that there was a cluster of cells ahead with tops to FL600 and thunderstorms east of SLC, resulting in a lot of holding, and suggested that they amend their routing and proceed direct to Thurman (TXC), Myton (MTU), which would take the flight south of its original routing as it flew east to west around Denver. He also noted that he sent them turbulence plot (TP) CN11. The captain reported that the revised routing would have put them directly toward a gap in the weather that he observed on the weather radar.

A review of ATC transcript information from between 0129 and 0141 revealed that four other aircraft traveling westbound to various destinations in the western United States at similar altitudes were making significant deviations to the north and south around the weather developing in western Nebraska. At 0141, the ZMP controller again informed the flight crew of the large area of moderate-to-extreme precipitation at their 12-o'clock position and 130 miles out and advised them of the decisions of the other flight crews headed in that direction to deviate well north or south around the area of precipitation. The captain then requested to proceed direct to TXC, MTU, then as filed, per the dispatcher's suggested routing around the weather. The controller cleared the flight as requested, and at 0143, instructed them to contact the Denver ARTCC (ZDV).

About 0143, the captain contacted ZDV and asked about the approaching weather and if any other flights had gone through it or if they had deviated north or south to get around it. According to the captain, the ZDV controller advised upon check in that the sector had just opened up, and the captain stated he believed that indicated that the weather might have been improving. The ZDV controller did not provide the weather conditions but advised the flight crew of a "hole," or gap, in the weather, which was on about a 240 to 245-degree heading that he felt they could get through with some deviations.

About 0154, the pilot of eastbound Southwest Airlines flight 3318, which had just passed through the hole in the weather in the opposite direction, provided a pilot weather report (PIREP) to the ZDV controller indicating that the hole was starting to close and that he did not think anybody should go through it behind them. The ZDV controller did not provide this PIREP to the incident flight crew. Also about 0154, as the incident flight was about 50 to 60 miles from the weather, the pilot of eastbound American Airlines flight 1155, which had passed the incident flight earlier in the opposite direction, reported a dramatic temperature increase at cruise altitude. According to the incident captain, he also noted a temperature increase at cruise altitude, followed by a "rough ride" and "static discharge," and he briefly could not hear the radio due to the static.

At 0200:42, the captain informed the ZDV controller that he wanted to turn around and requested a southerly heading. The ZDV controller instructed the flight to turn left to a heading of 115°. At 0201:11, the ZDV controller advised the captain that he was turning toward a cell to the south and asked him to let him know if that was not going to work.

According to flight crewmember interviews, about 0202, as the they turned the airplane left, the weather radar display began to indicate red. The flight crew chose to turn right, and the flight subsequently encountered hail, which shattered the outside panes of both of the airplane's forward windows. The captain declared an emergency, and due to the noise associated with the hail striking the airplane and windshield, assumed the PF duties and began a descent to FL230. The flight crew diverted the airplane to DEN, landed at 0242, and arrived at the gate at 0255. PERSONNEL INFORMATIONThe flight crew consisted of two pilots and three flight attendants. The flight crew was based in Minneapolis, St. Paul, Minnesota. The incident occurred during the first leg of the third day of a four-day pairing.

The captain, age 57, held a valid Federal Aviation Administration (FAA) airline transport pilot (ATP) certificate with a type rating for the Airbus A320. The captain held a first-class medical certificate with a limitation to have glasses for near vision, and he had his glasses for the incident flight.

The captain was originally hired by Northwest Airlines in January 1989. He had been an Airbus captain for about 11 years. According to Delta Air Lines, his total flight time was 16,628 hours, 13,846 hours of which were in Airbus airplanes and 5,818 hours of which were as pilot-in-command.

The first officer, age 44, held a current ATP certificate with a type rating for the A320. The first officer held a first-class medical certificate with a limitation to wear glasses, and he was wearing his glasses during the incident flight.

The first officer was originally hired by Northwest Air Lines on October 30, 2000. He had been flying the A319/320 for about 4 years. According to Delta Air Lines, his total flight time was 4.682 hours, 922 hours of which were in Airbus airplanes.

The assigned flight dispatcher was originally hired by Delta Air Lines on September 27, 1977. He began working for Delta Air Lines cleaning airplanes before eventually pursuing training and placement as a flight dispatcher and had been certified for more than 30 years.

The ZDV air traffic controller was originally hired by the FAA in July 2011. After completing initial ATC training, he was assigned to ZDV and was certified in January 2015 on the radar position he was working at the time of the incident.

A review of the FAA Program Tracking and Reporting Subsystem (PTRS) database showed no records or reports of any previous aviation incidents or accidents involving the captain or first officer. AIRCRAFT INFORMATIONAccording to FAA records, the incident airplane was an A320-211, registration number N332NW, serial number 319, registered to Delta Air Lines. The airplane was powered by two CFM56-5A1 engines. At the time of the incident, the airplane logbook contained one deferred item for the auxiliary power unit. The airplane was dispatched with a maximum landing weight of 142,198 pounds, and it landed at DEN with an estimated weight of 130,718 pounds. METEOROLOGICAL INFORMATIONThe National Weather Service (NWS) issued a severe thunderstorm watch for the incident site and surrounding area at 2105 with severe weather possible through 0500. Further, the NWS issued a severe thunderstorm warning for the area north of the airplane's flightpath as early as 0133, at which time the incident aircraft was still in ZMP airspace about 230 miles east-northeast of the developing thunderstorms they later encountered. The NWS Storm Prediction Center (SPC) day 1 convective outlook that was issued and valid before the incident flight crew received their preflight weather information forecast areas of severe weather along the flight route. The NWS area forecast issued before the incident flight received their preflight weather information also mentioned thunderstorms, possibly severe, along the flight route. Neither the NWS SPC day 1 convective outlook nor the area forecast were provide...