As seasonal hazards go, avoiding thunderstorms makes the first page of our risk avoidance playbook this time of year. Thunderstorms in the free MMOPA Flight Risk Assessment Tool (FRAT) app earned the highest risk number in the app at “8.” It’s safe to say the hazard is well-known.

Growing up, most of us learned quickly not to put our hand on a hot stove. It seems intuitively similar we should also respect thunderstorms. Yet the PA46 community experienced 12 fatal accidents, claiming 32-lives over the years. It’s been pretty evenly divided: 5 Mirages, 3 Malibus, 2 JetPROPs and 2 Meridians. Of the last three, all were non-radar equipped Malibu airframes. The pilot in the last accident specifically told ATC he was using NEXRAD for weather avoidance.

Convective storms contain every weather risk imaginable; wind, turbulence, lightening and icing. Fortunately, most of the fleet is equipped to help us identify/avoid the threats. So where are we going wrong?

Most of the final NTSB reports focus on l the pilot’s efforts to circumnavigate the problem, many relying on the controller’s weather picture. Communications usually end abruptly as Mother Nature demonstrates her superiority.

“We’ve Got Problems…”

We traced one Meridian accident in 2007 to a pitot heat failure (N477MD) while encountering convective activity.

About 0750, N477MD departed KSUS and was initially cleared to climb to 4,000 feet. The controller advised of light to moderate precipitation 3 miles ahead of the aircraft. The pilot requested a northerly course deviation for weather avoidance, which was approved. The controller then advised of additional areas of moderate and heavy precipitation ahead of the airplane, gave the pilot information on the location and extent of the weather areas, and suggested a track that would avoid it. The pilot responded that he saw the same areas on his onboard radar and concurred with the controller’s assessment.

The pilot contacted the ZKC controller at 0800:47, and after a discussion about the final requested altitude, was cleared to climb and maintain FL230. At 0801:42, a position relief briefing occurred, and the controller was replaced. The new controller made no transmissions to N477MD and was replaced by a third controller at 0806:27. The next transmission to N477MD occurred at 0812:26, when the controller asked the pilot if he had been given a clearance to deviate. The flight’s radar track showed that the airplane turned to the left. The pilot responded, “mike delta we’ve got problems uh…”

The controller responded by asking the pilot if he was declaring an emergency and made several other attempts to contact N477MD. The pilot did not respond to any of these calls, and radar contact was lost. None of the three ZKC controllers had given the pilot any weather information during the time he was controlled by ZKC.

From the NTSB report: The pilot’s PFD airspeed data dropped from about 142 KIAS to zero about 0810:45 and the co-pilot’s PFD airspeed dropped from about 140 KIAS to zero about 0810:51. The airplane climb rate decreased as the PFDs’ airspeed data dropped to zero and about 0811 the airplane’s heading started to turn to the left from the straight track. About 0811:04 on the pilot’s PFD and 0811:06 on the co-pilot’s PFD, non-zero airspeed values were recorded for approximately 25 seconds and approximately 10 seconds respectively before the recorded data indicated zero again on both PFDs. The data showed that airplane’s engine was operational and that there was no reduction in power as the airplane started the left turn. About 0812:30, the data showed the airplane had achieved a 250-knot ground speed and then sustained two vertical accelerations about 5g. 

Both PFDs’ airspeed, vertical speed, and altimeter display data validity bits switched to a fail state. A red X is flagged over displayed parameters that have failed validity bits.

The pilot would have relied on the standby instruments without benefit of the standby airspeed indicator due to the inoperative pitot heat.

Vo Explained

The two vertical accelerations of 5 g’s mentioned above is a key point in this discussion. Unless you’re an aerobatic pilot or a military fighter pilot, you probably have not and will never experience a 5 g acceleration. If your airplane weighs 4,000 pounds, the wings would have to support 20,000 pounds at 5 g’s. If you weigh 200 pounds, well you get the idea.

Our fleet has published maximum positive load factor speeds (+3.6 to + 3.8) depending on the model and much lower negative load factors (-1.48 to -1.52) again based on the model. The maximum negative load factor with the flaps extended is zero. To that end, many have installed G-Meters to keep track albeit after the fact.

To address it preemptively, we have Va (maneuvering speed) and Vo (maximum operating maneuvering speed).

Vo is a selected (not necessarily computed) speed that must not exceed a value related to stalling speed. According to 23.1507, Vo is a speed where the airplane will stall in a nose-up pitching maneuver before exceeding the airplane structural limits. This is actually closer to the definition of “maneuvering speed” than the common usage of Va, but is distinguished from “turbulent air penetration speed” by being related to a control force, not a force imparted by outside forces, i.e., wind shear.

Simply put: SLOW DOWN. The wings bend/break when excessive lift is applied to the structure. Weight is fixed. Speed controls lift. Flaps add lift so leave them up. You and your co-pilot may be tempted to argue whether you should use Va/Vo in severe turbulence. Or maybe not. Simply slow down to around 100 KIAS and extend the landing gear for stability. Do not attempt to maintain altitude as changing pitch affects load factor. Maintain attitude (shiny side up) and accept altitude changes.

Most of our inflight breakup NTSB reports included references to straight line speeds well in excess of the Va/Vo.

No sane pilot would intentionally fly into convective activity so one must assume what you see in front of you was unforecasted. How bad is that storm?  Quantifying the danger is a real challenge: light green, dark green, light yellow, orange, red? Common avoidance practices dictate at least 20 nm from cells and at least 40 nm between cells.

A little more than 70 percent of the PA46s were delivered with a capable radar package (Sorry Norm, I don’t include the Malibu’s in-wing weather scout radar). Unfortunately, too few pilots understand its capabilities or how to use it to their advantage. Training providers can do little more than address it academically unless the weather happens to cooperate. Your association and its safety and training foundation responded to member requests and included radar educational programs at the convention and at locations around the country. If you weren’t fortunate enough to attend, additional video resources are available from:

Bendix King RDR 2000: https://youtu.be/O4UxlOBvTkI

Garmin GWX 68: https://buy.garmin.com/en-US/US/p/207#accessories

Download on the page.

There is also a popular handout from Malibu Aerospace.

Radar is great for short-term decisions (tactical), but it can’t see behind Mother Nature’s Mask. That’s where NEXRAD (satellite delivery) and/or ADS-B (ground-based delivery) prove their strategic benefit. The combination of radar and NEXRAD/ADS-B can be extremely effective. The NEXRAD/ADS-B latency issue is well-known and has been identified as a causal factor in several GA accidents, including at least two PA46 inflight breakups.

From the NTSB Safety Alerts…

What Can Pilots Do?

1. Remember that the in-cockpit NEXRAD display depicts where the weather WAS, not where it IS. The age indicator does not show the age of the actual weather conditions but rather the age of the mosaic image. The actual weather conditions could be up to 15 to 20 minutes OLDER than the age indicated on the display. You should consider this potential delay when using in-cockpit NEXRAD capabilities, as the movement and/or intensification of weather could adversely affect safety of flight.
2. Understand that the common perception of a “Five-minute latency” with radar data are not always correct.
3. Get your preflight weather briefing! Having in-cockpit weather capabilities does not circumvent the need for a complete weather briefing before takeoff.
4. Use all appropriate sources of weather information to make in-flight decisions.
5. Let your fellow pilots know about the limitations of in-cockpit NEXRAD.

Onboard technology is incredible. Add that to ATC guidance and you should be able to come up with a safe plan (which may include turning around).

Limitations to ATC

Things to consider when getting ATC weather vectors: Approach control radar reports 4-levels of precipitation; light, moderate, heavy and extreme. Center radar reports moderate, heavy and extreme precipitation. The center radar system is called WARP (Weather And Radar Processor). The radar products are further divided into altitude segments so be sure the controller provides the info appropriate for your altitude. In fair weather WARP gets refreshed every 11-minutes. In precipitation mode, the updates are every six minutes. A lot can happen in six minutes.

In both cases, the systems only report precipitation. They don’t see turbulence or clouds, including building/mature cumulonimbus.

You, on the other hand, can provide/request pilot reports. A note: PIREPs from airliners are probably from airspace well above you and they may be overflying treacherous weather at your operating levels.

In my experience, ATC is extremely helpful but may be constrained by traffic. When requesting deviations, offer them options such as “unable deviations to the left but, we can do 15 degrees right.” You still have the option of “doing a 180” and don’t hesitate to let them know. I’ve heard the “180” is only successful about 30 percent of the time, primarily because pilots take too long to implement it. The other choice is declaring a weather emergency. This unties the controller’s hands and gives them more tools to help.

There’s an old saying: If the pilot makes a mistake, the pilot dies. If the controller makes a mistake, the pilot still dies. The pilot is responsible for the safety of the flight and can do whatever is necessary to ensure a safe outcome.

Additional Threats

Convective icing can be sudden and devastating. In the cumulous building stage, moisture is drawn up into the cloud faster than it can freeze, becoming supercooled. Our aircraft provides a perfect collecting surface and can quickly be overwhelmed. A common practice is to avoid entering any cumulus cloud above the mid-teens.

Lightening is also a concern. The average airliner gets hit about once a year and our ships get hit as well, thankfully not as often. The hit usually has an entry point, typically the prop, and an exit point, usually the wingtip, flight control surface or the vertical stabilizer. I know of one instance where it struck the prop and exited the vertical stabilizer. Repairs to the airframe were minor and the insurance paid for the engine/propeller teardown/repair.

A dissipating thunderstorm often generates a significant outflow referred to as a gust front. In extreme cases, these can reach surface speeds of more than 65 knots. In July 2011, N46TW attempted to depart ahead of an approaching storm. The gust caught up with the plane as it turned crosswind resulting in a sudden loss of airspeed, a stall spin and a tragic loss of life.

Radar and NEXRAD/ADS-B are great, not to mention pretty, but we often base our decision to continue by how dark the clouds look and is there light at the end of the tunnel (at least in the daytime). I rely extensively on my “ocular radar” (my eyeballs) and my wife Suzanne for the real-time weather evaluation and we avoid convection by a wide margin.

In Summary

• The most expensive equipment can be rendered useless by poor judgment;
• Learn your equipment’s capabilities and limitations;
• If the success of the flight depends on weather avoidance equipment; do you really need to go?
• Lester Kyle’s weather axiom states: “Fly Away from the Red”

Sage advice!

by Dave McVinnie

Dave McVinnie is a 20-year Master Flight Instructor, FAAST Representative and a Designated Pilot Examiner with over 11,000 hours and 33-years of instructional experience. He was selected as CFI of the Year in 1995, 2009 & 2014. Dave currently serves on the MMOPA Safety Committee and has specialized in the PA-46 for the past 17-years. McVinnie Aviation offers insurance accepted initial and recurrent training, including initial instrument training. For more info, go to McVinnieAviation.com