ERA12LA500

The pilot's failure to avoid an encounter with known adverse weather conditions, which resulted in an in-flight upset, temporary loss of control, and loading of the airframe, engine, and propeller that led to the in-flight separation of the propeller and the subsequent forced landing. The root cause for the separation of the propeller could not be determined based on the available information.

The pilot reported that he was conducting a cross-country instrument flight rules flight, and, during the cruise portion of the flight, he intermittently encountered areas of instrument meteorological conditions (IMC). About 1 hour 50 minutes into the flight, an air traffic controller advised the pilot of an area of moderate-to-extreme precipitation 20 miles ahead, extending along the intended route of flight for 100 miles. Eight minutes later, the pilot contacted an air traffic controller and requested a descent from 12,000 to 10,000 ft mean sea level (msl) "for weather," but he did not receive a reply to the request, and the airplane continued on-course. After an additional 8 minutes, the pilot reattempted to contact a controller but was interrupted by another pilot, and he again received no response. The pilot attempted to contact a controller a third time and requested a turn to get out of the weather. This time a controller responded and advised the pilot to turn left, but, just as the pilot initiated the left turn, the airplane encountered an area of severe turbulence. The pilot reported that, while in the turbulence, the airplane encountered an updraft that put the airplane in a 4,000 ft per minute climb and that the airspeed reached 253 knots, which exceeded the airplane's never-exceed airspeed. The airplane then encountered a downdraft, which caused the airplane to lose 3,000 ft of altitude, and the primary flight display simultaneously "went black." When the display returned, it showed a message advising the pilot to "level the wings" while the attitude and heading reference system realigned. The pilot subsequently used the standby instrumentation to control the airplane while he initiated an emergency descent. The airplane exited the turbulence and IMC about 4,000 ft msl, and, shortly thereafter, the propeller separated from the engine. The pilot subsequently performed a forced landing to a cornfield, and the airplane sustained substantial damage to the fuselage and both wings. The pilot reported that he received a weather briefing before departing on the accident flight. According to audio recordings of the briefing, the weather briefer advised the pilot of the adverse conditions along his route of flight; the pilot replied, "Ok, I guess we'll deal with that when we get there, if we have to go around it or stop, that's fine." An air traffic controller again advised the pilot of the severe weather conditions at least 20 miles ahead of the encounter. It is unlikely that the pilot's initial unanswered request to descend to 10,000 ft msl would have prevented the weather encounter, and the pilot's second and third unsuccessful attempts to contact the controller occurred more than 15 minutes after he was first advised of the weather conditions. The pilot was clearly made aware that severe weather conditions existed along his route of flight, but he waited until too far into the flight to try and avoid them, which ultimately led to the flight's encountering the conditions that resulted in the in-flight loss of control. The air traffic controller complied with the Federal Aviation Administration's minimum requirement for "additional services" by providing the hazardous weather information to the pilot when he first checked in, but additional information by the controller would have been valuable. For example, as the flight continued tracking directly into known heavy-to-extreme precipitation that other aircraft were deviating around, the controller should have realized that the pilot was not taking action to avoid the weather and either suggested a deviation or at least updated him about the proximity of the hazardous weather that the airplane was rapidly approaching. Regardless, it was ultimately the pilot's responsibility to avoid the severe weather. The propeller hub was found detached from the airplane due to a failure caused by reverse bending fatigue of the mounting bolts connecting the hub assembly to the engine crankshaft mounting flange. All of the bolts exhibited features consistent with fatigue cracking in a circular direction along the same direction as the wear marks on the hub case aft face. The reverse bending failure of the hub mounting bolts was indicative of a loose connection between the hub and the crankshaft. None of the airplane's documented maintenance indicated that the propeller hub was removed during the year before the accident. The engine's fractured connecting rod exhibited a small thumbnail fatigue crack on one side. However, this small amount of fatigue likely occurred after the fatigue cracking had begun on the propeller bolts. Cracking in the propeller bolts would likely have created unbalanced loading in all of the connected components, including the crankshaft and connecting rod. Once the propeller separated from the crankshaft, the crankshaft absorbed the entire load exerted by the engine, and this increased loading likely in turn increased the friction at the contact surfaces beyond the capacity of the lubrication. Without sufficient lubricating capacity at the journals, the material would begin to heat excessively, creating local material deformation. The underlying reasons for the loose connection between the propeller hub and the crankshaft could not be determined, but it is likely that the extreme forces encountered during the flight's weather-induced upset and loss of control resulted in the ultimate failure of the connecting bolts.

Air Traffic Controller Interviews Each of the four air traffic controllers working the airspace surrounding the accident events was interviewed separately. The Radar Associate Controller (RA) stated that when he assumed his position, the accident pilot already on frequency and recalled that there had been a lot of deviation requests by other aircraft as a result of the weather. He next observed the accident flight had lost approximately 800 feet of altitude and had passed that information along to the Radar Controller (RC) to ensure he was also aware. He said the RC then instructed the Radar Developmental (RD) controller to ask the pilot what his altitude was, and the accident pilot replied that he had encountered heavy turbulence and advised he was unable to maintain altitude. The RA then initiated a "point out" with FLO approach control and advised them that the accident flight was unable to maintain altitude. According to the RA, the FLO approach controller then, after referencing other traffic, approved the point out and stated that the accident flight was radar contact. The RA also stated that he continued to relay the status of the accident flight with FLO throughout the event. When asked, the RA did not recall seeing the accident flight tracking towards the adverse weather, and did not recall the accident pilot requesting to deviate around weather until he had already encountered the heavy turbulence. He felt that, often, the weather information displayed on the radar display was not accurate, or was very slow to update. When asked to elaborate, he stated that he believed there was a 15 minute delay for Weather and Radar Processor (WARP) data to update on the radar display screen. Because of the delay, he stated it was not common to suggest deviations around weather or to suggest headings without a pilot's request to deviate. He stated that he did not recall the cloud tops at the time, nor did he remember the accident pilot being asked for a pilot report (PIREP). As he recalled, the accident flight was the only low flying aircraft in the sector around the time of the accident. He stated that he did not know what type aircraft the flight was, but assumed it was a single engine prop based on the speed. The RD controller recalled that upon initial check in, he issued the accident pilot the current weather. He remembered there being heavy precipitation along the west side of the sector. He recalled the accident flight encountering weather and the accident pilot requesting to deviate. He thought he had issued a turn to a heading of 090, at which point the pilot stated he had encountered severe turbulence. He then noticed that the pilot had lost several thousand feet very quickly and the pilot stated he had lost his AHRS. He stated that the RC controller then assumed responsibility of the position and training was discontinued. He recalled the RC controller asked the pilot if he could maintain altitude and it was shortly after that the pilot reported he had lost engine power. He said the RC controller then issued the pilot a heading to FLO, and after the flight had turned toward the airport, the pilot reported that he was not going to reach the airport, and would have to put it down in a field. The RD controller further stated that there had been airliners diverting around the adverse weather for quite some time. He felt the deviations correlated accurately with the weather being displayed by WARP at the time, but said pilots do not always request to deviate so he generally did not ask pilots if they would like a deviation around weather. He stated that general aviation pilots would routinely fly through weather that was displayed on radar, so he did not find it odd that the accident flight was continuing toward the displayed weather even though airliners were deviating around it. He said that WARP data really "wasn't that great," but that it was better than nothing. He estimated WARP latency to be 5-10 minutes. When asking for updated weather, he stated that he would ask pilots rather than the front line manager since he felt pilots had a better idea of current weather conditions than someone on the ground did. The RC recalled that when the accident pilot checked in, the RD controller advised the pilot of the precipitation being shown via WARP and also read the current AIRMET to him. The next time the RC recalled hearing from the accident pilot was when he asked for a vector out of the weather. The RD controller instructed the accident pilot to make a left turn and, when able, proceed direct to CHS. The RC then noticed the accident flight had lost altitude and asked the pilot if he was able to maintain his altitude. When the accident pilot advised he was unable to maintain his altitude, he discontinued training on the position and took over for the RD controller. He stated that he then issued the pilot a heading to FLO, and the pilot stated he would not be able to make it to the airport and would be landing in a field. The RC said it was common for airliners to deviate around weather, but that some typically general aviation pilots would still fly through, so he did not find it unusual that that the accident flight was flying opposite direction of all the deviating airliners. He said that by the time the accident pilot called for a heading to get out of the weather he was already visibly in it according to displayed WARP data. He said he had not heard the accident pilot request a descent to 10,000 feet and if he had, stated he would have approved it. He initially issued a frequency change to the accident pilot once he had reported out of the weather and felt that he was in stabilized flight and FLO had reported that he was visible on radar. He said that due to frequency limitation at low altitude in that area, he felt it would be better to put the pilot in contact with the receiving facility in order to maintain communications with him until landing. Pilot Interview During a post-accident interview, the accident pilot stated that the airplane's G-500 received automatic updates from NEXRAD, and that the typical latency was between 1 to 200 minutes. The G-500 indicated the displayed data was three minutes old just prior to entering the thunderstorm. He said he used the Garmin information as a "situational awareness tool." On the MFD (Multi-Function Display) he could access winds aloft and METARS, which he used for flight planning. The aircraft was also equipped with traffic advisories, but he was not monitoring it at the time. The aircraft previously equipped ADS-B, but he generally was not satisfied with the information it provided. He was pleased with the G-500 and felt that the manuals were user friendly and easy to understand. He generally had more confidence in the weather data that ATC had than what was available to him in the aircraft. Prior to the flight he filed his flight plan online, checked the weather on the NOAA website, and received a weather briefing from the Lockheed Martin Flight Service. He thought he had an hour to make it to his destination before weather moved in and was prepared to divert and wait out the weather if he needed to. He stated that enroute, the 48 knot actual headwinds were much greater than the forecasted headwinds of 25 knots. He had planned a fuel stop at XFL, but did not have an alternate because the weather at his destination did not require one. He had 74 gallons of fuel onboard, which would have given him a five hour range, for the four hour flight. He said that in general he received good service from ATC in previous trips along the same route of flight, although that was mostly in VFR conditions. He usually requested and received flight following because of all of the warning areas along that route of flight. On the day of the accident his initial attempt to contact ZJX went unanswered; when he called a second time ATC advised him there was light to moderate precipitatio