- Location: Centerville, Tennessee
- Accident Number: DCA25LA197
- Date & Time: May 2, 2025, 12:00 Local
- Registration: N247WN Aircraft: Boeing 737
- Aircraft Damage: Substantial
- Defining Event: Windshear or thunderstorm
- Injuries: 149 None
- Flight Conducted Under: Part 121: Air carrier - Scheduled
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/200101/pdf
https://data.ntsb.gov/Docket?ProjectID=200101
On May 2, 2025, at 1200 pm central daylight time, Southwest Airlines flight 2231 (SWA2231) encountered turbulence and hail during initial descent into Nashville International airport (BNA), Nashville, Tennessee. The flight was a regularly scheduled passenger flight from AustinBergstrom International airport (AUS) to BNA. As a result of the hail, the airplane sustained substantial damage to the leading edges of the wings and horizontal stabilizer. The flight continued to its destination without further incident.
The flight crew reported that thunderstorm activity was forecast for their arrival at BNA, and they observed weather approaching the airport using a weather application (WSI app) on their electronic flight bag (EFB). They planned and conducted a deviation to the north to avoid the weather. As the airplane passed the Memphis area, the captain asked the flight attendants to be seated early in the event of unforeseen turbulence.
Prior to the encounter, while descending from flight level (FL) 360 toward FL240, the flight had been in clear air and the flight crew could see a cloud build-up at their 1:00 o’clock position. Air Traffic Control (ATC) also advised of “a cell” at their 12:30 to 1:00 o’clock position. However, after reviewing the on-board weather radar and the WSI app on the EFB, those sources did not depict any indications of weather directly ahead of the airplane. As the descent continued, the flight crew noticed below and ahead of the airplane was a flat stratus cloud layer, with no buildups. ATC advised of moderate to extreme precipitation at their 12:30 to 1:00 position, which the crew associated with the buildup they had visually seen at their 1:00 o’clock position.
SWA2231 entered the clouds at about FL320 and initially the ride was smooth, with occasional light chop. While at a speed of 290 knots, at FL280, SWA2231 suddenly encountered precipitation and turbulence. The captain recalled that the rain was very heavy and the excessive noise caused him to suspect hail, but he was unable to verify visually. He retarded the throttles and deployed the speed brake to slow to turbulent air penetration speed. After about 1 minute the heavy precipitation ceased, and the airplane levelled off at FL240, still in instrument meteorological conditions. The flight crew reported the moderate turbulence to ATC and continued to BNA.
A review of weather records revealed that the National Weather Service’s (NWS) Aviation Weather Center had issued Convective SIGMET 99C at 1155 which was extended over the area for an area of severe embedded thunderstorms, moving from 250° at 40 knots, with maximum tops above FL450. Hail to one inch in diameter and wind gusts to 50 knots were possible with the storms. The NWS Storm Prediction Center had issued a severe thunderstorm weather watch at 0956 for a line of severe thunderstorms moving across Tennessee.
Figure 3 shows the nearest WSR-88D weather radar base reflectivity image for the for 3.12° elevation scan at 1202, with SWA2231’s flight track position overlaid at 30 second intervals. The flight passed through an area of extreme intensity echoes up to 65 dBZ at lower elevation scans and 58.5 dBZ at the airplane’s flight level. The severe hail algorithm indicated hail to 1.58 inches in the vicinity of the flight track during the period with the maximum height of the 18.5 dBZ echoes or echo tops to FL446.
Figure 4 is a software analysis cross section of the WSR-88D imagery at 1202, with the approximate flight track of SWA2231 overlaid in white and depicting the flight overflying a maximum reflectivity core of 60 dBZ and in echoes of 56.0 dBZ along the track.
The reason that the severe weather depicted in figures 3 and 4 was not depicted by the onboard weather radar system or the WSI app was not determined. The first officer did not recall the onboard radar system tilt setting(s) used at the time, and the onboard radar imagery was not recorded. The operator had no means to replicate which imagery was available to or used by the crew from the WSI app. The Federal Aviation Administration’s Aviation Weather Handbook notes the following about airborne weather radar:
The radar display also does not provide assurance of avoiding instrument weather conditions from clouds and fog. A phenomenon called attenuation (see Section 15.2.5) may exist when a cell absorbs or reflects all of the radio signals sent by the radar system (see Figure 15-5). Attenuation may prevent the radar from detecting additional cells that might lie behind the first cell. This is sometimes referred to as a radar “shadow.” For aircraft equipped with airborne weather radar, pilots are expected to be familiar with the operating techniques and limitations of the specific system.
It is important to note that while hail always gives a radar echo, it may fall several miles from the nearest visible cloud, and hazardous turbulence may extend to as much as 20 mi from the echo edge.
The severe weather may not have been depicted to the crew on their resources due to radar limitations or the specific settings of the onboard radar (such as tilt and range), rapid development and/or movement of the severe weather, latency in the data provided by the weather application, or other factor(s). There was insufficient evidence available to determine if any of these characteristics were a factor or not.
- Probable Cause: An encounter with hail during descent.
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