Citation III; VI; VII (C650)
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 94; Flight Crew Total 8920; Flight Crew Type 839
Human-Machine Interface
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Diverted; Flight Crew Landed As Precaution; General Declared Emergency; General Maintenance Action
Weather; Aircraft
We were flying north-east bound at FL410; flying from the southwest. I was the Captain; and the First Officer was flying. We were above an under cast flying toward a rapidly developing line of weather that stretched from the Southwest through Western Midwest [and then] from the West turned south and continued. Our aircraft is equipped with both on-board weather radar as well as NEXRAD radar imagery provided via XM through a Garmin GPS. Our weather briefing before takeoff showed the tops of the weather at around FL250; an altitude that we could easily top. By the time we reached the area about an hour later; convective SIGMETs had been issued reporting the tops approaching FL450. As we approached the line; we were able to visually see tops of the individual cells. Comparing our visual analysis; both radars; and suggestions from ATC; we came up with our plan for getting to the east side of the weather. The southern line of weather was several miles behind the southwest line; so we decided the safest plan was to fly east; past the southern line; then turn to the south-southwest to pass through the gap between the two lines. While we were flying east; the on board radar showed a gap between two cells directly ahead. We could see both cells visually as well. We considered continuing straight ahead; versus our original plan. About that time we entered the under cast and visibility became nil. We requested FL430 multiple times; but were unable to climb due to traffic. Neither the NEXRAD nor ATC radar showed the gap we were seeing; so we decided to continue with our original plan and began a turn to the southwest. As we took up our southwesterly heading; the on board weather radar failed. During the next few minutes; we flew west-southwest; to get to the gap based on the NEXRAD and ATC advice. We requested a climb to FL430 or FL450; but were denied again due to traffic. Also; as a result of the weather and multiple aircraft deviating; the center frequency was very congested. After getting handed off to Center; it took between 5-10 minutes to check-in with Center As we approached the gap on the NEXRAD; we began a turn back to the south. Suddenly we encountered increasing turbulence; with 3 to 4 hard jolts of turbulence; followed by a strong updraft. The autopilot disconnected due to its inability to overcome a strong updraft. I assumed control of the airplane and hand flew the aircraft throughout the remainder of the event. We encountered possible severe turbulence and began an uncommanded; uncontrolled climb. We advised ATC; declared an emergency due to our inability to control altitude. We were granted clearances to FL430 and FL450. We climbed to FL450 in under a minute. Immediately we encountered a downdraft; and were cleared to a lower altitude. In addition to the altitude fluctuation; the turbulence continued to be moderate verging on severe. The episode took only two to three minutes; and we ended up flying eastbound and were cleared to descend to FL390. A couple of airliners followed our rough track; and also reported severe turbulence. As we exited the weather; the right-hand Chip Detector annunciator illuminated. According to the checklist; it is an advisory indication and suggests shutting down the engine if the conditions allow. All other engine instruments indicated normal; so we elected not to secure the engine. At this time we were approximately 150 miles to a en route airport; and decided to land there to have the engine looked at. Post flight examination revealed minor lightning strike damage to the radome; both wing tips; and the fuselage fuel tank drain mast. In all there were about half a dozen dime size or smaller spots evident of lightning. Having discussed the flight with the First Officer; we agreed that there were several circumstances that contributed to our weather encounter. The most obvious was the failure of the on board radar. The on board radar is the best source of information about the locationof storm cells. Losing it left us effectively blind. Frequency congestion; virtually everyone in the controller's sector was deviating; leading to an abnormal amount of radio chatter. This delayed our ability to make course changes and collaborate with ATC about the weather their radar was painting. Also; it made it difficult to report the loss of radar; and get extra assistance in circumnavigating the weather. Inability to climb to a higher altitude; we were weight limited to FL410 on takeoff. As we burned fuel; we requested FL430. Unfortunately due to other traffic; we weren't able to climb. Had we been able to climb to FL430 or 450 we most likely could have maintained visual separation from the storm cells; NEXRAD lag. Knowing that NEXRAD data is not current; we had to make our best educated guess as to where the well defined gap showing on the NEXRAD actually was located. It's also possible that if part of the line in front of us was dissipating; the on board radar showed the gap before the NEXRAD. The NEXRAD showing the solid line contributed to our decision to turn rather than fly straight ahead as described earlier in the narrative. There were no injuries to any of the three passengers; just a few spilled drinks. The Citation Service Center found a bearing casing in the accessory gearbox that had half of the case coming apart. It was their belief that this was not caused by lightning and had likely started at an earlier date. Whether or not the deterioration was sped up by turbulence is inconclusive. As a precautionary measure the Service Center also inspected the aircraft for severe turbulence and found NO damage. The engine has been repaired; the minor lightning damage repaired; radar replaced; and aircraft has returned to service.
[Narrative #2 contained no additional information.]
While attempting to avoid a line of thunderstorms and at FL410 using NEXRAD and on board Radar; A CE650 flight crew experiences a Radar failure and severe turbulence resulting in altitude excursions. An emergency is declared and the flight is cleared to FL450 then eventually down to FL390. Upon clearing the weather the RH Chip Detector illuminates and the crew elects to divert for maintenance.