Meteorological Conditions Associated with Bell-206 LR4 Aircraft Accident near

Kahramanmaras, Turkey,

On 25 March 2009

Fatma EMİN

Abstract

An Bell-206 LR4 aircraft crashed near Kahramanmaras, Turkey, on 25 March 2009 killing all 6 people on mountain. The Helicopter was carried Muhsin YAZICIOĞLU who was a politician man the leader of Great Union Party (BBP) and a journalist was name Ismail Gunes. After crash Gunes called 112 emergency to informed them about crash and asked for help but they could not help because of difficulties of visibility and high elevation of mountain. After 48 hour the crash local people found the debris of helicopter and 6 people’s lifeless body between Sisne and Kızılöz village of Keş mountain of Kanlıcukur place. Available weather data, including those from a Geostationary Operational Environmental Satellite,Turkish Meteorological State synoptic data, instability indexes and a passenger’s report have been examined in combination with analysis fields from the Forensic Aviation Meteorology. Synthesis of this information provides a relatively complete and consistent picture of the ambient meteorological conditions in the region of the Bell-206 LR4 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 unslope flow and light winds, as indicated by cloud-top temperatures of -10° to -15°C.

1. Introduction

The crash occurred mountain of Kesdagı and its elevation is 572m above sea level these elevation causes data is not suitable for the investigation. This investigation include gathering and plotting atmospheric data to establish the state of the atmosphere at the time of the occurance, during the flight. The purpose of this study is to evaluation that causes the accident in synoptic scale meteorology by reconstructing the weather of the day of the accident. This is accomplished by compiling data from both homogenous and non-homogenous observational records, from available weather data and contemporary pubilitions. Through this

reconstruction, it is possible to infer some characteristics of the general pattern of weather conditions. Weather analysis checklist for aircraft accident investigation provides a sound, logically flowing analytical framework to facilitate identification of flight conditions and allow for detailed analysis of the plotted atmosphere data to enable investigators to identify if, and what, meteorological factors played a role in accident causation.

Analyses checklist is;

a. Stabilityb. Cloudc. Weatherd. Visibility

e. Wind-Windshearf. Turbulanceg. Icingh. Density Altitude

According to Hüseyin Günes’s report there was severe fog on the ground of mountain and severe surface snow. Considering with these information I evaluate the forensig analyses checklist.

Though it is important to understandthat meteorological conditions and phenomena influenced the aircraft. It is also important to understand pilot decision in relation to weather. By having a detailed understanding of meteorological conditions present at the time of occurrence, in flight and pre flighting investigation will be better able to understand situations encountered by pilots as well as operational desitions that comes out of them. Kaya Istektepe who was the pilot of helicopter has had same severe health problem (SHGM, report).

A letter from R.Briot(vice president of flight operations, ATR support, Inc.) dated 23 August 1995, states the following:” Without your ability to study the available meteorological data, we would still probably be looking for some improbable combination of structural failures, despite all the information given by a state of the art flight data recording system. Our swift progress was made possible thanks to your previous and unique experience in this field of science.”

The primary objective of this paper is to combine all data and infer meteorological conditions considering with I.Gunes’s report.

Section 2, discussed meteorological parameters effect on aircraft. Section 3

presents the meteorological data and analyses relevant to crash. Section 4 represents the conclusion.

figure 1 elevations of stations around crash

2. Effects of meteorological conditions on aircraft

General Aviation (GA) accident statistics indicate that visual flight rules (VFR) flight into instrument meteorological conditions (IMC) is a major safety hazard within general aviation.

All of the meteorological factors are important of flight but fundamentals are; clouds and sky cover, density altitude, icing, precipitation, pressure altitude, snow depth, state of the ground, surface wind, temperature, visibility and turbulence. Clouds are always major consideration for aviation operations. Low overcast clouds will limit the effectiveness of aerial illumination devices. Density altitude is a critical measurement that determines if an aircraft has enough lift capabilities and performance to get off the ground. Too much density altitude limits fuel, weapons, and passenger loads.  Ice on lifting surfaces affects the aerodynamics of the aircraft. Even a little ice is a big

problem. Rain and snow affect visibility and the safety of both crew and airframe. In some instances, precipitation may cause predestination of munitions. Pressure altitude computed figure affects all aircraft engine performance. Snow compounds ground handling problems. Light, powdery snow may interfere with helicopter hover operations. Ground conditions impact on the effectiveness of serially delivered munitions. Surface winds; strong winds, especially cross-winds, affect aircraft control near the ground during take-off and landings. They also affect ground speed for low-level frights. High temperatures reduce lift capability. Cold temperatures increase maintenance requirements and the time needed to accomplish each task. The number of personnel that can be carried on a flight is reduced due to the weight of cold-weather gear. Thunderstorms and lighting Extreme weather that includes thunderstorms and lightning is very hazardous to in flight operations, refueling, and rearming operations. Turbulence Severe weather and clear air turbulence is a critical condition affecting all aviation assets and missions. It may cause aircraft structural damage or even crashes during take-offs and landings. Severe turbulence may cancel all operations. Visibility: The lack of good visibility affects landings and take-offs, visual reconnaissance, target acquisition, E-O target designation, terminally

guided munitions, and the ability to distribute scatterable mines. Winds aloft: winds at flight altitudes always affect navigation and fuel consumption.

3. Meteorological analyses using forensic analysis checklist

Synoptic overview:

figure 2 surface analyses chart

At the time of the Bell-206 LR+ crash, (1350 UTC 25 March 2009), a deep low pressure system is Northeast of the Turkey and 1012mb pressure line is on the kahramanmaras so do not expected frontal effect but this lead drought below normal temperatures. For the best analyses the same level with MGM (Turkish State Meteorological Service) charts is also on figure 3 show us omega block that cause dry weather and light wind for an extended period of time while rain and clouds are common associated with the two troughs on either side of the omega block.

Although omega block temperature was the 5°C and 4 °C on the 850mb map(1200 UTC-0000 UTC). The At 700mb the air was saturated over the south of Turkey. To the north , however The soundings at Adana (figure6) indicate a stable dry aair with dewpoint depression -8  °C or -10  °C.

figure 3

figure 4

figure 5

figure 6 500mb vorticity

figure 7

figure 8

At 500mb vorticity shows us small eddies in the atmosphere. The region of Kahramanmaras was lighter vorticity that means weaker eddies. The 300 mb chart shows the winds at 300mb level. The wind speeds are shown in color contours, the heights in solid black lines. Areas of strong wind Areas of strong winds at this level (winds >100 knots or 115 mph), commonly

referred to as jets, indicate areas of high atmospheric energy. These are created by strong temperature contrasts in the lower and middle tropopause and reflect areas of potential storm development. 

For the purpose of forensic analyses the checklist must be consider:

a.stability

Total total K ındex Lifted index

Showalter index

Sweat Cape Cın

51.30 25,90<30 1,51<3 3.26 203,7 25,98 -8,6Thunderst

orm probability is strong

Unstable air

Strong lifting,

stable but weak

convection

Stable but weak

convection

Slight severe

thunderstorm

PositiveMarginal

but unstable

air

Weak force for

LFC

According to stability of the air weather was the stable and there wa no precipitation or thunderstorm possibilities but dewpoint temperature and ambient temperature close each other that cause low level clouds was occur.

b. Cloud, Visibility and Fog

The place where was crash occur was mountain and this topographic features mainliy effect of the air flow that cause orographic lifting other terms that mean are upslope flow, topographic uplift and forced land lifting. When this type of lifting occurs the land forces the air to move to a higher elevation. Several thermodynamic variables change when air rises. The temperature of the air cools as air is lifted. In this situation it is common to notice cooler temperatures in the higher elevation regions and warmer temperatures in the lower elevation regions. As temperature cools, not as much moisture has to be evaporated into the air to reach the saturation vapor pressure. As air cools, eventually the saturation vapor pressure will drop to the actual vapor pressure and the relative humidity will reach 100%. When this occurs clouds and precipitation can develop. It is common for an

orographic lifting situation to produce cooler and damp weather especially if the air has to rise a significant vertical distance. The wind direction will determine which side of a high elevation region experiences orographic lifting. Since weather in the mid-latitudes tends to move from west to east it is common for the western side of high elevation regions to have significant orographic lifting.

The highest level of the mountain has snow cover and that is also effect the ambient temperature. Surface snow cover cools low temperatures from the values they would be. Three types of latent heat can be absorbed from snow and they are melting, evaporation and sublimation. During the day, just like clouds, snow cover is a good reflector of shortwave radiation from the sun. This is especially true of fresh snow. At night, snow cover is a good emitter of longwaveradiation.

Often record low temperatures occur on a night with surface snow cover. The sublimational and longwave cooling from the snow cover makes the low colder than it would otherwise would be. During the day, evaporation and melting promote cooling. This along with reflection keeps daytime temperatures cool. 

To obtain a more complete view of the mesoscale conditions over accident site, satellite data were used. the image show us the low level cloud this mean that the fog was over accident area and surface snow could be mainly cause of the icing.

In aviation visual meteorological conditions (or VMC) is an aviation flight category in which visual flight rules (VFR) is permitted that is, conditions in which pilots have sufficient visibility to fly the aircraft maintaining visual separation from terrain and other aircraft. They are the opposite of instrument meteorological conditions (IMC). The boundary criteria between IMC and VMC are known as the VMC minima and are defined

by: visibility, cloud ceilings (for takeoffs and landings), and cloud clearances.

figure 9

c.Wind Shear and Turbulance IcingAccording to Wyoming sounding it is clear that wind is not strong also GFS models show that is. These light wind do not allow dissipative fog and icing. Cloud droplets and liquid precipitation can remain liquid even when the air temperature surrounding the suspended or falling liquid is below freezing. This occurs because the liquid needs a surface to freeze upon. The liquid droplets will freeze without a nuclei surface if the temperature drops low enough. As a general rule, liquid cloud or precipitation drops between freezing and -10 C (14 F) will remain liquid. When the temperature drops to below -40 C, all liquid droplets will solidify. Droplets that are liquid and are below freezing are referred to as supercooled droplets. The possibility that supercuuled droplets were might be present strongly because of snow cover. It has been demonstrated that supersooled water droplets degrade aircraft performance. Summarized the effect of icing on flight by comparing the decrease in climb capability with the potential accumulation of ice on the craft , that is the total amount of supercooled liquid

intercepted by the aircraft. Regions with supercooled water droplets present were shown to have substantially greater effect than those with smaller,”cloud-size” droplets. Further analysis revealed that the main effect of ice accretion in SCDD environments was to increase the drag on the airframe. The extreme performance degradation due to SCDDs was further documented by Politovich (1989), who expanded the study to include more cases from different geographical regions. Politovich (1996) later found that the mere presence of large droplets, that is, droplet size distributions with MVD > 30 mm, was not sufficient to provide extreme decreases in flight capability on the Wyoming King Air. Liquid-water contents of > ~0.2 g m-3 were also needed; MVD > 30 mm in lower liquid-water contents produced performance degradation similar to that from smaller droplet encounters. Environments with high liquid-water contents at temperatures warmer than -10°C can also result in extreme performance degradation, as suggested by the data analyzed by Politovich (1996) and by numerical simulations such as those by Shin et al. (1991). This cannot be ruled out as a possibility in the Bell206 case; available data suggest temperatures

between 0° and-8°C and liquid-water contents of at least 0.3 g m-3.However, the meteorological data are also highly consistent with the scenarios found to be associated with supercooled water droplet formation.

5.ConclusionsSupercooled drizzle drops (SCDDs) were likely to have been present in the ATR72 holding patternwhich was located near the tops of stratiform clouds that had cloud-top temperatures of -10° to -15°C and substantial vertical wind shear (0.016 s-1). NEXRAD radar and radar wind profiler data, as well as output from the RUC objective analysis, support this conclusion. This case also suggests that the dry slot in a comma cloud may be a preferred location in midlatitude cyclones for SCDDs because the subsidence or advection of high-momentum dry air can remove the upper snow clouds that would otherwise rapidly deplete the SCDDs through seeding. Under certain conditions, the temperature, moisture, and wind shear profiles in this region could readily combine to create conditions conducive to SCDD formation by an enhanced coalescence process. At the time of the accident, little basis existed for predicting SCDDs aloft. The Pobanz et al. (1994) study had not been published, and the significance of SCDDs produced by wind shear in the absence of a warm layer along with the implications for hazardous icing had not yet been realized. It should be noted that wind profiler data had only recently become available and that the RUC model and NEXRAD radars had only recently come on line as part of the NWS

modernization. Therefore, there was no basis to forecast SCDDs aloft in this area. The statistical relation between vertical wind shear and SCDDs has not yet been independently confirmed, nor is there a viable physical explanation for the statistical relationship. Although WISP investigators have discussed a possible nowcasting and verification project for SCDDs, the possibility of determining where and when in the life of a storm SCDDs are likely to occur had not been seriously considered until the Bell206 crash.

ReferancesAshenden, R., and J. Marwitz, 1996: Supercooled large droplet distributions in the natural environment and comparison to artificial drizzle from the air force water spray tanker. Proc. of the FAA Int. Conf. on Inflight Aircraft Icing, Springfield, VA, FederalAviation Administration, (DOT/FAA/AR-96/81, II), 33–43.

Pobanz, B., J. Marwitz, and M. Politovich, 1994: Conditions associatedwith large-drop regions. J. Appl. Meteor., 33, 1366–1372.

Sand, W., W. Cooper, M. Politovich, and D. Veal, 1984: Icingconditions encountered by a research aircraft. J. Climate Appl.Meteor., 23, 1427–1440.

1996: Response of research aircraft to icing and evaluationof a severity index. J. Aircraft, 33, 291–297.