NTSB Factual Report

HISTORY OF FLIGHT

On March 5, 1998, about 0520 central standard time, a Cessna 208B, N840FE, registered to Federal Express Inc., and operated by Baron Aviation Services, Inc., as flight SM8315 (call sign Show Me), was destroyed after impact with the ground, near Clarksville, Tennessee. The commercial-rated pilot was fatally injured. Instrument meteorological conditions (IMC) prevailed in the vicinity, and an IFR (instrument flight rules) flight plan had been filed. The scheduled domestic cargo flight from Memphis, Tennessee, to Bowling Green, Kentucky, was being conducted in accordance with Title 14 CFR Part 135. The flight had departed Memphis, at 0413.

The pilot of SM8315 was in radio contact with air traffic controllers at the FAA Memphis Air Route Traffic Control Center (ARTCC) and was level at an altitude of about 9,000 feet, on the Nashville VOR 315-degree radial, about 25 nautical miles, when radio and radar contact was lost. Witnesses in the area reported hearing the sound of the crash and the wreckage was located a short time later. The crash site was located on the Nashville VOR 315-degree radial about 35 nautical miles, or about 5 miles southeast of Clarksville.

The last radio communication with the pilot of SM8315 was at 0447, when he checked in on frequency with the Memphis ARTCC, and reported at 9,000 feet. About 0520, radar contact was lost. At 0521, the controller attempted to re-establish radio contact with the pilot, and said he had lost his transponder. No response from the pilot was received, and no further radar contacts were made. The airplane impacted in rough terrain, at a steep angle of impact.

Two other company pilots flying in the same vicinity at the time of the accident said they were at 7,000 feet msl (SM8314), and 5,000 feet msl (SM8316). They said they were in and out of the clouds. The pilot of SM8314 indicated that the outside air temperature (OAT) at 7,000 feet was between 0 degrees C (32F) and -1 degree C (30F). The pilot of SM8316 indicated that the OAT at 5,000 feet was between 3 degrees C (37F) and 5 degree C (41F). The other two company pilots also said they had radio contact with the pilot of SM8315 about 5 minutes before the accident. They said he sounded fine and did not say anything about any problems. A third company pilot flying about 100 miles behind SM8315, said he was at 9,000 feet and had picked up some ice crystals. The third pilot landed at Nashville, about 50 miles south of the crash site.

Radar data showing the flight's ground speed indicated that at 0512, the ground speed was 158 knots (182 mph). The ground speed then decreased to 153 (176 mph), 143 (165 mph), 138 (159 mph), and 132 (152 mph), until at 0519:40, when the ground speed of the flight was 125 knots (144 mph). After the radar readout at 0519:40, the next radar hit was "coast," no information, and then the flight disappeared from the radar scope. The sweep of the radar scope was 12-second intervals. During the change in ground speed the airplane's heading and altitude did not change.

The NTSB Office of Research and Engineering's Radar Data Study revealed that radar trajectory studies indicated the flight was cruising at about 9,200 feet msl (mean sea level) altitude and at roughly 135 knots (156 mph) calibrated airspeed (KCAS) en route from Memphis to Bowling Green. According to the NTSB Radar Data Study, calculated flight parameters indicated the airplane "...experienced a slow reduction of airspeed in the final 8 minutes of flight at altitude, and then abruptly exhibited a sharp nose down pitch attitude with a rapid increase in airspeed."

Radar plots showed that SM8315, "...maintained a steady altitude at 9,400 feet-msl, at an airspeed of close to 135 knots, and flying on heading 040 [degrees]. About 10 minutes before the upset...the aircraft's airspeed began to slightly reduce to close [to] 125 knots [144 mph] as the pitch angle and flight path remained steady. Five minutes before radar contact was lost, [the] airspeed began to further reduce at an increased rate, with a corresponding increase in angle of attack. About the time of the increased reduction in airspeed, pitch angle began to slowly increase also. When radar contact was lost, the calculated airspeed had reduced to less then 102 knots [118 mph], and calculated body angle of attack [AOA] had increased to 8.8 degrees. A large reduction in pitch angle, angle of attack, and flight path angle as the airspeed increases after peak AOA was reached." (See the NTSB Radar Data Study an attachment to this report.)

A witness, who had an aviation background, was located at his home about 1 mile south of the crash site. He told investigators he heard an aircraft directly above his house "at approximately 200 feet, having engine trouble. " He described the sound from the airplane as like the sound of a "pilot changing the prop setting [pitch angle]." He then heard the airplane crash.

The accident occurred during the hours of darkness approximately 36 degrees, 28 minutes north, and 087 degrees, 13 minutes west.

PERSONNEL INFORMATION

Information on the pilot is contained in this report on page 3, under First Pilot Information. The pilot had been employed by Baron Aviation Services Inc., for 7 1/2 years, with a date of hire of August 13, 1990. The company reported it was common practice for their pilots to fly the same route, and the majority of this pilot's time with the company was flying the same route as the accident flight. The duty time of the pilot on the day before the accident, March 4, 1998, was 7 hours 51 minutes. On the day of the accident, March 5, 1998, the pilot had a duty time of 6 hours 23 minutes. The pilot had a total flight time in this make and model airplane of 5,198 hours. His last check ride before the accident was February 26, 1998.

AIRCRAFT INFORMATION

At the time of the accident the total time on the airframe was 4,078.5 hours. The maximum gross weight was 8,750 pounds. The airplane was equipped with leading edge deicing boots on the wings, elevators, struts, and had a cargo pod deicing capability. Lights were installed to illuminate the leading edge of the wings, to aid the pilot in detecting ice on the leading edges of the wings during night operations. The airplane was not equipped with an ice detection device.

METEOROLOGICAL INFORMATION

Meteorological information is contained in this report on page 3, under Weather Information. A preliminary weather study for the accident area showed that at 9,000 feet the temperature was minus 4 degrees C (24.8 F), and the tops of the clouds were from 10,000 to 11,000 feet. There was also an AIRMET (Airman's Meteorological Information) issued that covered the area around the crash site that called for icing conditions.

The following AIRMET was found in the wreckage; "AIRMET ICE...Tennessee, Mississippi, Alabama...FROM TRI TO CHA TO 50W ATL TO GWO TO DYR TO TRI, LGT OCNL MOD RIME ICGIC BTN 060 160. CONDS OVR NRN MS /WRN TENN, SPRDG TO RMNDR AREA BY 09Z...CONS CONTG BTD 09Z THUR 15Z."

[From Bristol/Johnson/Kingsport, Tennessee, to Chattanooga, Tennessee, to 50 miles west of Atlanta, Georgia, to Greenwood, Mississippi, to Dyersburg, Tennessee, to Bristol/Johnson/Kingsport, Tennessee, light occasional moderate rime icing between 6,000 feet msl and 16,000 feet msl. Conditions over northern Mississippi/ western Tennessee, spreading to the remainder of the area by 0900 UTC (0300)...conditions continuing beyond 0900 UTC thru 1500 UTC (0900).] A map trace of this AIRMET, showed that it included the flight path area, times and altitudes associated with the flight of SM8315.

The pilot of SM8314 said that his flight conditions at 7,000 were, "...IMC [instrument meteorological conditions] with an outside air temperature of 0 degrees C (32F) to -1 degree C (30 F), but no ice was forming on my airplane at any time."

At the request of the NTSB investigator-in-charge (IIC), additional questions in reference to the flight condition were asked of the pilot of SM8314, May 1998, by a Federal Express, Aircraft Safety Investigator. He was asked, "...did [he] take any anti-ice precaution? He answered: "Yes, he turned on the pitot-static heat and was watching for ice build up on the wings via ice detector light mounted in the left wing leading edge-to-fuselage fairing." The second question the Federal Express, Aircraft Safety Investigator asked the pilot, "...[if he was] aware of the AIRMET for ice in Tennessee, Mississippi, Alabama, covering portions of his route from Memphis to Bowling Green?" He answered, "...yes, he obtained the same weather information as the mishap pilot [SM8315], that particular AIRMET was included in the weather briefing and he was aware of it."

Upper air wind data was obtained for Nashville, Tennessee, at 0600, on March 5, 1998, located about 41 nautical miles southeast of Clarksville, and was chosen for its proximity to the crash site. The data obtained shows the height in meters mean sea level (meters times 3.2808 equals feet), temperature, dew point, wind direction (degrees true), wind speed (meters per second), level (pressure millibars). The following was determined for altitudes between 2,134 meters [7,001 feet msl] and 3,009.5 meters [9,874 feet msl]. (See the NTSB Radar Data Study attached to this report.)

Altitude 2,134 meters [7,001 feet], the temperature was -1.5 degrees C [about 28 degrees F], dew point -2 degrees C [about 28 degrees F], wind direction 280 degrees, wind speed 7.2 meters per second, pressure 781.5 millibars.

Altitude 2,439 meters [8,002 feet], the temperature was -3 degrees C [about 27 degrees F], dew point -3.5 degrees C [about 27 degrees F], wind direction 290 degrees, wind speed 7.7 meters per second, pressure 752.2 millibars.

Altitude 2,743 meters [8,999 feet], the temperature was -4.4 degrees C [about 25 degrees F], dew point -5 degrees C [about 23 degrees F], wind direction 295 degrees, wind speed 11.3 meters per second, pressure 724.1 millibars.

Altitude 2,765.8 meters [9,074 feet], the temperature was -4.5 degrees C [about 24 degrees F], dew point -5.1 degrees C [about 23 degrees F], wind direction 295.4 degrees, wind speed 11.5 meters per second, pressure 722 millibars.

Altitude 3,009.5 meters [9,874 feet], the temperature was -5.1 degrees C [about 23 degrees F], dew point -18.1 degrees C [about 0 degrees F], wind direction 300 degrees, wind speed 13.3 meters per second, pressure 700 millibars.

Altitude 3,156.7 meters [10,357 feet], the temperature was -5.5 degrees C [about 22 degrees F], dew point -16.5 degrees C [about 3 degrees F], wind direction 300 degrees, wind speed 14.2 meters per second, pressure 687 millibars.

The NTSB Meteorological Factual Report revealed that at 0515, about 5 minutes before SM8315 was lost on radar, the radiative temperature in an area centered at Clarksville (4 kilometer resolution data), in degrees Kelvin (K), showed that the mean radiative temperature was 266.9 degrees K, or -6.26 degrees C (21F). The minimum radiative temperature was 266.5 degrees K, or -6.66 degrees C (19F). The maximum radiative temperature was 267.1 degrees K, or -6.06 degrees C (21F). [Note: 273.16 degrees Kelvin (K) = 0 degrees C. To convert degrees K to degrees C, the following formula was used; C = (K - 273.16)]

According to the NTSB Meteorological Factual Report, addendum, the weather data taken from an Archive Level II Doppler weather radar tape from Nashville, Tennessee, revealed that the Plan Position Indicator (PPI) image for a beginning sweep time of 0508:10, showed that SM8315 had tracked into a weather echo from 0510:34, to 0516:28. The NTSB Radar Data Study had shown that the speed of the airplane began to decrease at 0512, and the last radar readout was at 0519:40.

The maximum weather radar reflectivity along SM8315's track was 10.0 dBZ (Note: dBZ is a measure of the weather radar echo intensity. dBZ = 10 LOG Z .. where Z = the concentration of uniformly distributed small water particles that would return the amount of power received. Z is in millimeters to the sixth power divided by meters cubed. Given dBZ = -1.0 results in Z = 0.1. Given dBZ = 60 results in Z = 1,000,000. A dBZ value of -1 to 2 is a weak weather echo. A dBZ value of 60 is an extreme weather echo. A value seen in thunderstorms).

The Table below relates dBZ to weather echo intensity.

Table A

dBZ Intensity

<0 to 29 Weak 30 to 39 Moderate 40 to 44 Strong 45 to 49 Very Strong 50 to 54 Intense 55 or greater Extreme

Cross-sections of weather radar reflectivity (dBZ) were prepared for the airplane's track data for several points along the flight path. The cross-section at 0505:18 showed no weather echoes above 7,000 feet. The cross-section at 0514:00, showed weather echo tops about 9,000 feet, from 0513:28 to 0514:28, and a weather echo top about 7,700 feet at 0515:28. The maximum weather echo intensity at 9,000 feet was about -1.0 to 2.0 dBZ. The cross-section for 0519:50, showed no weather echoes above 7,000 feet.

The Doppler Weather Radar data, revealed that SM8315, had entered a weak weather echo about the same time that the speed of the airplane started to decrease, and the airplane was in the weak weather echo for a few minutes. Based on the weather data, it was determined that in-flight airplane icing conditions were encountered by SM8315. The NTSB Meteorological Factual Report and attachments are attached to this report.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy was performed on the pilot, on March 6, 1998, at the Medical Examiner's Office, Nashville, Tennessee, by Dr. Charles H. Harlan.

Toxicological tests were conducted at the Federal Aviation Administration, Research Laboratory, Oklahoma City, Oklahoma, and revealed, "No ethanol detected in Blood." Drugs, "...0.007 (ug/ml, ug/g) Tetrahydrocannabinol Carboxylic Acid (Marihuana) Detected in Kidney Fluid...0.01 (ug/ml, ug/g) Tetrahydrocannabinol Carboxylic Acid (Marihuana) Detected in Blood."

The toxicology report was reviewed by the NTSB Medical Officer, Washington, D.C. According to the Medical Officer, the drugs found indicates only that the pilot used marijuana in the "previous days or weeks." The remote marijuana use indicated by the toxicology findings almost certainly had "no direct" effect on the ability of the pilot to "operate the aircraft."

COMMUNICATIONS

According to the Air Traffic Control (ATC) transcripts of communications, SM8315 was issued an IFR clearance to Bowling Green, by Memphis ATC Clearance Delivery, at 0350, and was cleared for takeoff from runway 18L, at 0413. Communications between SM8315 and ATC were routine. The pilot of SM8315 reported on frequency at an altitude of 9,000 feet. He then requested and received a direct routing to Bowling Green. At 0447:05, the pilot of SM8315 was instructed by the Memphis ARTCC (Air Route Traffic Control Center), to "contact Memphis Center 125.85," and the pilot acknowledged the transmission.

At 0447:15, the pilot of SM8315, contacted the Memphis ARTCC Bowling Green Low Altitude Radar Control Position (R41) and said, "...Show Me 8315 level niner thousand."

There were no further transmissions until 0521:16, when the ARTCC controller called SM8315, and said, "...Show Me 8315 I've lost your transponder sir."

The ARTCC controller tried to call SM8315 again and did not get a response. The controller then contacted Show Me 8314 (SM8314), and at 0522:02 said, "...Show Me 8314...can you do me a favor and make a radio check to 8315, I've lost his transponder about ten miles in front of [you], I have no radar target any longer I'd like to see if you can get him on your frequency." SM8314, acknowledged, and attempted to call SM8315 on the company frequency, as well as the ATC frequency, without any success.

At 0522:31, the R41 controller called Nashv

NTSB Probable Cause

the pilot did not maintain control of the airplane due to undetected airframe ice, resulting in an inadvertent stall, and subsequent impact with the ground. Factors in this accident were; flight into clouds, below freezing temperatures, and the inability of the pilot to detect ice, due to the lack of an ice detection system to determine ice build up on portions of the airframe that are not visible from the cockpit.