Updated: Nov 22, 2022
On the morning of November 9, 2022, the pilot and passenger of a Piper Malibu Meridian (N234PM) was fatally injured in an accident while on approach to North Platte Regional Airport/Lee Bird Field (KLBF) according to local news reports. According to FlightAware (below), the flight departed Lincoln Airport (KLNK) at 8:32 a.m. CST and it was headed west to North Platte, Nebraska. Local news reported that the crash occurred at 9:29 a.m. CST and a post-impact fire occurred.
The NTSB will be visiting the site and will likely issue their final report in about a year from the date of the accident. There are a lot of potential factors to cause such an accident that may or may not include weather. However, as will be discussed below, serious icing conditions were indeed present in the area and this accident may be associated with an encounter with nonclassical freezing rain. Let’s walk through the analysis to see if this is likely.
Update: You can view the preliminary NTSB accident report here. No new information that really points to a cause. The pilot was vectored to the ILS for runway 30 and was given the proper clearance and descent for the approach. Approach control gave the pilot the instruction to change over to the North Platte advisory frequency prior to the accident.
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According to the FlightAware track log, the pilot climbed to the cruising altitude of 16,000 feet MSL after departing Lincoln. Given the low IFR (LIFR) conditions at North Platte, the aircraft was likely vectored to an instrument approach at KLBF. The routine observation issued at 1453Z reported north-northeast winds, surface temperature of -1°C, 4 statute miles surface visibility with an overcast ceiling of 300 feet in light freezing rain (-FZRA) as shown below.
KLBF 091453Z AUTO 02009KT 4SM -FZRA BR OVC003 M01/M02 A2993 RMK AO2 UPB37E51FZRAB51
Shortly after the accident, a surface observation from the Automated Surface Observing System (ASOS) shown below reported similar conditions that included light freezing rain. This was a completely automated report. In the remarks it appears to have been intermittent reports of unknown precipitation type (UP) that began at 35 minutes after the hour and ended at 40 minutes after the hour. This is likely the case where freezing drizzle may have been occurring. An ASOS can not automatically report freezing drizzle and will usually report an unknown precipitation type instead. Note that UP is unknown precipitation type, not ice pellets.
KLBF 091546Z AUTO 03008KT 4SM -FZRA BR OVC003 M01/M02 A2993 RMK AO2 UPB35E40FZRAE1456B40 P0000 I1000 T10061017
As shown below, a surface cold front with a strong temperature gradient was was passing through the North Platte region around 0600Z and moving to the southeast. This was approximately 9.5 hours prior to the accident. At 0600Z, the winds were brisk from the south-southeast and the surface temperature was a mild +19°C (66°F). The sky was reported as clear below 12,000 feet.
KLBF 090553Z AUTO 17016G26KT 10SM CLR 19/14 A2985
By 1500Z (10 a.m. CST) or 30 minutes prior to the accident, the cold front had passed well to the southeast of the airport (below) and was slowing down and at 1500Z was analyzed as a stationary front. The winds shifted to the north-northeast in the overnight hours and the surface temperature fell to -1°C (31°F) at the time of the accident.
A nonclassical freezing rain/freezing drizzle signature was present at 1500Z as shown below in the Rapid Refresh (RAP) model analysis. The surface temperature is below 0°C with a shallow surface-based temperature inversion through 5,000 feet MSL (the elevation at KLBF is 2777 feet). The winds near the surface were from the northeast bringing in cold, dense air with winds aloft primarily from the southwest or warmer flow. This creates this shallow temperature inversion to form with warm air overrunning cold air at the surface.
With dry conditions aloft and cloud depth of roughly 4,000 feet, this upglide over the that cold air was giving rise to very light precipitation. Given the warm cloud tops, the only possible precipitation type here is freezing rain or possibly freezing drizzle. Drop sizes are likely between 100 and 500 microns. This would imply a median volumetric diameter (MVD) of > 50 microns which is well into the supercooled large drop (SLD) icing regime. SLD is also depicted in that area from the Current Icing Product (CIP) analysis valid at 1500Z for 3,000 feet MSL.
However, the subfreezing layer was extremely shallow in the sounding analysis above...on the order of 500 feet. On an instrument approach, the aircraft would have likely been on short final at 500 feet.
Lastly, the amended terminal forecast for KLBF at 1242Z was not of much help and did not indicate the potential for freezing rain.
KLBF 091242Z 0913/1012 02010G18KT P6SM OVC008
FM091800 15014G28KT P6SM BKN035
FM100000 16021G35KT P6SM SCT050
TEMPO 1004/1006 3SM SHRA OVC030
FM100600 31018G28KT P6SM OVC020=
Unless the subfreezing layer was deeper than suggested by the sounding analysis above, it is unlikely that icing was to blame for this accident. This assumes, of course, that the pilot was flying the instrument approach as charted and didn't descend below minimums while on the approach. Also, the aircraft surfaces would have been fairly warm given the temperatures aloft were well above freezing.
There were no G-AIRMETs issued at the time of the accident. There was an IFR G-AIRMET issued along with a G-AIRMET for nonconvective LLWS. Given the stable conditions near the surface, it is unlikely that this was a turbulence related event.
Most pilots are weatherwise, but some are otherwise™
Dr. Scott Dennstaedt
Weather Systems Engineer
CFI & former NWS meteorologist