Date: 201809
Local time of day: 1201-1800
Location: ZFW.ARTCC, TX
Weather elements / visibility: Windshear; Thunderstorm; Turbulence; 10
Light: Daylight
Aircraft: Bonanza 35
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZFW
ATC / advisory: Center ZFW
Aircraft component: Safety Instrumentation & Information
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Contributing factors: Weather; Human Factors; Aircraft
Primary problem: Weather

Narrative: After deviation for a growing TRW (thunderstorm) around BRK VOR Denver Center had cleared me direct to destination TKI. When entering FTW Center airspace they cleared me direct to GREGS intersection for the GREGS8 arrival. Approximately 100 NM northwest of GREGS second Controller noted moderate rain on my route of flight to which I replied there wasn't any visual or datalink indication of any rain at that time. Controller said the next controller would have more information. I asked that controller if I could proceed direct to TKI as that would take me east of the buildup area and was told; 'no I cannot approve that request.'Approaching the area described it appeared that tops were about 15;000' so I wasn't too worried as I was VFR at the time with scattered clouds below. Approximately 40 miles northwest of GREGS next Controller's transmissions were barely readable to me and I told him so but he was so busy with airline traffic diverting to avoid buildups by that time he didn't respond or if he did I couldn't hear him. It appeared the tops were probably about 20;000' but my datalink XM weather showed no rain or lightning and my storm scope showed no lightning in the area but by now I am flying through the area of buildups. I contacted the controller and asked for deviations to the left of course which he approved and gave me direct to GREGS when able. As I made about a 15 degree to the left to miss a buildup and then started a turn even further the left it appeared I was going to be in cloud in a few seconds and decided to turn off the altitude hold and pitch on the autopilot to hand fly the aircraft and seconds later although still clear of clouds I noted my altitude was about 11;350'. When I pushed the nose down while pulling the power back to 15 in. of MP (Manifold Pressure) [it took some time] to get back to 11;000' because of the thermal I was in. Shortly thereafter controller cleared me to 7000' and offered a heading of 090 to stay totally clear of the area but by that time I was through the first line of buildups and was able to proceed direct to GREGS. That was about the time the first indication of rain showed up on the XM display. During this whole process the update time on the XM receiver showed an update time of 3 minutes. Since I've been flying for over 50 years and have a lot cross country time I have experienced very rapid buildups of thermal activity before but this was one of the quickest I've seen. I think my decision to turn off the autopilot was a good one but if I could have been able to contact the controller to ask for a 1000' block altitude would have kept me from deviating the 300' rule. I felt really sorry for the controller involved because there was no way for him to receive all the calls he was getting from the all the pilots and from some of their conversations when they did reach him it was apparent they had made deviations on their own and then checked in with the controller telling him what they had done - all a pretty scary situation. Shortly after being cleared to 6000' and being mostly in the clear on my way to GREGS I noted the controller was offering to vector aircraft on the north side of the line directly to the east as he had offered to me. I'm sure by that time the line had filled in with no gaps and most pilots probably took the offer. I feel that rather than trying to keep aircraft on the arrival route it would have been much better to vector the traffic off the arrival route to a point in space where they could be turned back towards their destination than put everyone through the rapidly building storm. If the Controller I had asked for a deviation direct to TKI had allowed that request it would have been one less aircraft to be in the mix for the last Center Controller.




Synopsis: BE35 pilot reported encountering thunderstorms enroute that were not displayed in a timely manner on his XM weather datalink.