Meteorological Conditions Associated with the ATR72 Aircraft Accident near Roselawn, Indiana, on 31 October 1994

Abstract

An ATR72 commuter aircraft crashed near Roselawn, Indiana, on 31 October 1994 killing all 68 people on board. Available weather data, including those from a Next Generation Radar, a radar wind profiler, a Geostationary Operational Environmental Satellite, and pilot reports of icing have been examined in combination with analysis fields from the Rapid Update Cycle model and forecast fields from the Pennsylvania State University/National Center for Atmospheric Research MM5 numerical model. Synthesis of this information provides a relatively complete and consistent picture of the ambient meteorological conditions in the region of the ATR72 holding pattern at-3.1 km above mean sea level. Of particular interest is the evidence that these conditions favored the development of supercooled drizzle drops within a strong frontal zone, as indicated by cloud-top temperatures of-10° to-15°C, weak radar reflectivity, and strong, vertical wind shear within the cloud and warm front.

The Greenland Flow Distortion Experiment

“…Problems with severe icing (see the "Icing" sidebar) during a descent in flight B274, about halfway through the campaign, led to us adjusting some of our later flight plans. In order to prevent key instruments ICING S evere icing accumulation on any aircraft can be a serious safety concern (e.g., Marwitz et al 1997), while for instrumented aircraft any icing can cause instrument malfunction. During GFDex icing conditions were prevalent-we were often flying in clouds with supercooled water droplets and below-freezing air temperatures-and moderate icing occurred on four flights (B274, B276, B277, B278).…”

A climatological study of surface freezing precipitation in Europe

“…Following Marwitz et al (1997) and Strapp et al (1996), different types of idealized vertical thermodynamic profile were considered to explain the formation of freezing precipitation, as shown on Figure 8. The features of the different idealized profiles have been exaggerated.…”

“…For example, real profiles sometimes show slightly positive surface temperatures (between 0 and 2°C), whereas the surface temperature is shown as negative on Figure 8. In particular, a cloud top temperature between 0 and -10°C and a surface temperature warmer than 0°C is a hazardous in-flight icing situation (Marwitz et al, 1997).…”

“…In particular, it became apparent that special attention must be paid to the detection of the conditions leading to severe icing, which happens when large supercooled droplets, with diameters in the range of approximately 40-400 µm and fall speeds of 5 to 160 cm s -1 (freezing drizzle), are present in the atmosphere along with negative temperatures (Marwitz et al, 1997). These conditions lie outside of the current regulations for certification of aircraft.…”

The role of air turbulence in warm rain initiation

“…Representation of cloud microphysical processes is a source of significant uncertainty in numerical weather prediction and climate models. Critical weather phenomena such as aircraft icing and freezing precipitation often result from warm rain processes, sometimes with deadly consequences (Marwitz et al, 1997;Huffman and Norman, 1988).…”