Avoiding thunderstorms is a simple question of life or death. VFR pilots avoid them visually, and IFR pilots flying in IMC use on-board weather radar to detect and avoid them, it’s that easy. That being said, what is the need for a lightning detector, a.k.a. Stormscope ? Lightning occurs only in mature cumulonimbus, but these clouds also represent a danger for light aviation earlier in their development. Stormscope measures the distance to the strike on the base of the received power, assuming that all strikes dissipate the same energy, which is obviously not the case. Stormscope can take a strong and distant strike for a weaker but closer one, and vice-versa.

As you probably did not guess from the above, I’m a fan of Stormscope, and I’m not alone, given the number of units sold. As for all equipment, Stormscope is as good (or bad) as the pilot using it. Installing a weather radar in a single engine airplane is not easy, as the nose is usually occupied by the engine. The cost and weight of a radar also make it prohibitive for single engine piston aircraft. Single engine turbine is something else, as they are heavier, and operate at higher altitudes. While Stormscope is not a tool to avoid cumulus and CBs while flying IMC, it can bring precious information for strategic planing, and is in some respects better than radar.

It’s operation is easier (see the post from Sam in the links section of this post), and it provides information up to 200 Nautical Miles, on 360 degrees. Radar range depends of altitude, and detection usually covers an area from 45 degrees on the left to 45 degrees to the right. Evaluating the distance to a CB when flying VMC is not easy. Stormscope offers basic ranging, and valuable information about the development of the situation. When the screen becomes too populated with too many dots in the direction of flight, knowing what is going on behind the plane (in the airspace known as “escape route”, or “Plan B”) makes decision making easier.

The first time I changed from a Stormscope equipped plane to another one, I got a surprise: one was gyro-slaved, and the other not. This sounds like chinese to you ? Let me clarify that. When a strike occurs, the Stormscope measures its the range, and relative bearing, to display a dot on the screen. A gyro-slaved device receives heading from the flux-valve, so if the aircraft’s heading changes, the whole display is updated, so the position of the spots remains valid. With simpler (non-slaved) devices, the dots simply stay where they are. If you decide to turn because your Stormscope shows CBs in front, and don’t reset it, it’ll look the same after the turn… Here again, make sure that you know your on-board equipment, before you start your flight.

The picture below shows a classical (gyro-slaved) Stormscope. It is the small screen to the left of the control-colum, below the slip-skid indicator. The buttons control the range, and allow to clear the memory. This aicraft is equipped with a GNS430, but it was not coupled with the Stromscope.

Modern cockpits, like the G1000, allow for a full integration. The strikes can be displayed on the MFD, in a 90 or 360 degrees display, alone, or combined with map, topography, or terrain warnings. If you look in details the inset on the PFD on the second photo, you’ll see the Stormscope symbol, but not strikes (that was a nice day…).

A reminder about glass-cockpit integration. It’s not because strikes are displayed on a nice, wide screen, integrated with other information that the detection is more accurate. All the drawbacks and advantages I mentionned earlier relate to the detection technology (see the wikipedia entry in the links section), not to the display system. A wrong measurement remains wrong, even when displayed on the nicest screen in the world.

Interestingly, the conlusion is one more time the same: know your avionics, or it will kill you. Don’t mistake a Stormscope for a weather radar, know how to use it, build some experience, and you’ll remain on the safe side. This applies to so many things in aviation that it is probably a golden rule…

Read more:

Sam from Blogging at FL250 on using weather radar

AOPA Pilot paper (June 1997) about sparks detection

www.stormscope.net – have a look at the FAQ

Wikipedia, about lightning detectors

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