We train pilots to avoid thunderstorms: the FAA-approved distance from a storm is 20 miles. For a variety of reasons, that’s not always practical, and we can find ourselves well within 20 miles of a storm, engaged in some bobbing and weaving to avoid what we think are its worst areas. Those generally show red or purple (magenta? violet?) returns on a radar display. But when our weather radar data comes into our cockpit over a datalink, that’s a bad policy.
The main reason is the time it takes to aim a Nexrad antenna at a storm, collect the return data, process it into something visually useful to humans, and then pack and transmit the results to our airborne airplane. All that takes time. During that time, the storm likely has moved.
Which means datalink weather radar, including the FAA’s Nexrad information, available through ADS-B In’s flight information system-broadcast (FIS-B), is out of date when you see it. That’s true even if a time stamp on the display might indicate otherwise. In fact, both the FAA and NTSB—and this magazine—advise pilots to not rely on Nexrad for tactical thunderstorm avoidance. Use your Mark I, Mod I eyeball, instead, and remain outside the storm. If you stay in visual conditions, you can’t enter a thunderstorm.
Unfortunately, the fact that Nexrad data obtained over a datalink, including FIS-B, isn’t presented in real-time hasn’t filtered down to some pilots. Here’s an example of the worst that happen.
Background
On August 11, 2022, at about 1805 Eastern time, a Piper PA-32-301 Saratoga was destroyed when it broke up in flight and collided with terrain near Metz, West Virginia. The non-instrument-rated private pilot (male, 50) and two passengers were fatally injured.
The airplane departed Washington, Indiana, at 1543 with its base, Lebanon, Pennsylvania, as the destination. By 1752, the airplane was in cruise flight at about 9500 feet msl on an easterly heading, roughly paralleling a mixed band of precipitation stretching across Ohio, West Virginia and Pennsylvania. The pilot queried the Cleveland ARTCC and asked about a 30-degree left deviation through the precipitation. The controller replied, “I’m showing some slight gaps in that, but the whole line off your left-hand side is moderate to heavy with pockets of extreme. So, there may be some slight gaps. I’m just not real sure if they are in fact gaps from your point of view. But whatever you think looks good. Just let me know if you need anything.”
At 1801:09, the pilot announced a 20-degree left deviation. The controller indicated extreme precipitation just off the airplane’s left wing, with a small gap about five miles ahead. The pilot replied, “Yep, that’s what we’re looking for.” There were no further communications from the pilot. At that time, the airplane had entered an area of light precipitation.
It continued the same track over the next six miles, transitioning through radar echoes consistent with light, moderate, heavy and, finally, extreme precipitation. At about 1803, the track depicted a steep, descending right turn that continued until data was lost.
Investigation
The fuselage came to rest inverted with the engine and propeller still attached. The wings and tail section—including the horizontal stabilizer, elevator, vertical stabilizer and rudder—were separated from the fuselage. Several pieces of aircraft sheet metal were found along the wreckage path, with pieces associated with the tail section located the furthest from the main wreckage. The wreckage was distributed generally south of the fuselage over about 0.8 miles.
The left wing was about 100 yards to the west of the fuselage, and the right wing was about 400 yards southwest. Both wings were separated at their respective roots. The fractures were consistent with being overstressed. No pre-impact anomalies were found with the engine.
National Weather Service (NWS) forecast products revealed a chance of isolated thunderstorms over the area around the accident. The NWS had issued several advisories prior to the accident, including a center weather advisory and convective Sigmets.
Leidos Flight Service had no record of the pilot obtaining weather information associated with the flight; neither did ForeFlight. It could not be determined what, if any, weather information the pilot reviewed before or during the flight, other than the Nexrad weather data he discussed with ATC.
The pilot began flying in 2005 and had accrued 387 hours total time, of which 232 hours were in the accident airplane make and model.
The FAA web site supporting FIS-B notes that the weather information provided is for advisory use for the sole purpose of assisting in long- and near-term planning and decision-making. According to the NTSB, the Nexrad radar data on the display can be “up to 15 minutes older than the display’s age indication,” a disclaimer also stated in FAA Advisory Circular (AC) 00-24C, “Thunderstorms,” regarding the use of Nexrad data in the cockpit. The NTSB quoted from the AC: “Unlike airborne weather avoidance radar, weather data linked from a ground weather surveillance radar system is not real-time information. The radar data displays recent rather than current weather conditions. As the current location of a thunderstorm cell may be different than the broadcast weather product, do not attempt to find a hole in a thunderstorm solely using data-linked weather. Pilots must avoid individual storms by visual sighting or by airborne weather radar.”
Probable Cause
The NTSB determined the probable cause(s) of this accident to include: “The non-instrument-rated pilot’s intentional visual flight into instrument meteorological conditions based on latent weather information, which resulted in the airplane entering extreme precipitation, a loss of aircraft control, and in-flight break-up.”
According to the NTSB, “The non-instrument-rated pilot requested a deviation between what he described as a gap between radar echoes. The airplane subsequently transitioned through echoes consistent with areas of light, moderate, heavy, and then extreme precipitation before track data depicted a steep, descending right turn that continued until contact with the airplane was lost in the vicinity of the accident site.”
The NTSB added: “Based on his communications with air traffic control, the pilot was aware of the convective activity along his route of flight and was likely using his cockpit Next Generation Radar (NEXRAD) weather display for tactical weather avoidance decisions, and not accounting for the latencies inherent to the processes used to create and deliver this imagery to an inflight display.”
There simply is no good reason to fly into a thunderstorm. We’ll add, there’s no good reason to be in instrument conditions, if only briefly, if you don’t know what’s between you and clear air. That’s presuming you’re instrument-rated. Without the instrument rating, flying into any kind of IMC—especially in the vicinity of a thunderstorm—is foolhardy. We’ll never know if the pilot had done any of this before, but we do know he won’t do it again.
Timestamps, Nexrad And Latency
According to NTSB Safety Alert SA-017, In-Cockpit NEXRAD Mosaic Imagery, “The age indicator associated with the mosaic image on the cockpit display does not show the age of the actual weather conditions as detected by the NEXRAD network. Instead, the age indicator displays the age of the mosaic image created by the service provider. Weather conditions depicted on the mosaic image will ALWAYS be older than the age indicated on the display.” (Emphasis in original.)
How much latency should we expect? The NTSB’s Safety Alert states, “in extreme latency and mosaic-creation scenarios, the actual age of the oldest NEXRAD data in the mosaic can EXCEED the age indication in the cockpit by 15 to 20 minutes.”
