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On Wednesday morning, a small private plane ran into power lines in heavy fog over East Palo Alto, in Silicon Valley. The plane burst into flames and broke up, scattering fire onto a day care center, a home, and three cars, according to first responder reports. Killed in the crash were three employees of high-profile electric car maker Tesla Motors, based in nearby San Carlos.

Now, investigators for the National Transportation Safety Board — the same agency investigating the alleged mechanical problems in Toyota’s cars — is combing through the crash, looking for clues as to what happened. The NTSB has discovered that an electronic gunfire detection system installed in parts of East Palo Alto, famous for topping the nation’s per capita death ratings in 1992, picked up the sounds of the plane and its crash, according to an AP wire report:

The sound system was designed to help locate gunfire but also picked up the Cessna as it slammed into a set of power lines shortly after taking off in dense fog Wednesday, National Transportation Safety Board investigator Josh Cawthra said.

Cawthra said the recordings could give clues to any mechanical errors, allowing investigators to hear sound levels of the engine and propeller noise. It’s the first time he’ll use such data in a crash investigation.

East Palo Alto police installed a ShotSpotter system in late 2008. The ShotSpotter, which cost the city an estimated $200,000 or more, consists of a system of 16 to 20 specialized microphones installed over each square mile of the city covered.

ShotSpotter’s website has a blog post about Wednesday’s accident:

When we heard that a plane had crashed in an East Palo Alto neighborhood, all of us at ShotSpotter knew there was a high probability the city’s ShotSpotter Gunshot Location System had detected the incident.

ShotSpotter systems are designed to trigger only on loud, impulsive noises (loosely speaking, things that go “bang”). Sadly, yesterday’s plane crash created such a noise and it did trigger more than one ShotSpotter sensor deployed in East Palo Alto. Through subsequent filtering, the ShotSpotter system automatically classified the event as loud and impulsive but not gunfire and therefore correctly did not report the incident in real time to the East Palo Alto Police dispatch. However, for forensic purposes, all loud, impulsive noises are logged by ShotSpotter systems, even if they do not trigger an automatic alert, in case those noises needed to be reviewed after-the-fact. (Note: this only applies to loud, impulsive noises, of which there are relatively few per day in any given city.)

As with all audio associated with a ShotSpotter incident, the audio we assisted the East Palo Alto Police Department in providing to the NTSB starts a few seconds before the sound of the crash (providing the sound of the engines), includes the sound of the crash itself, and a few seconds after the crash. Because the ShotSpotter sensors each contain a GPS receiver with a precision clock, the NTSB now has a precise, millisecond-by-millisecond recording of the incident, as captured by several ShotSpotter sensors deployed throughout East Palo Alto. In total, five ShotSpotter sensors generated data which contribute consistently to the mathematical location of the crash. The sensors were located at various distances from the crash, the closest being just over 600 feet away and the furthest being roughly 1,500 feet away.

I couldn’t get the total number of sensors in East Palo Alto, but ShotSpotter’s head of marketing and sales said in a prepared statement that the system was installed in the most violence-prone neighborhoods. The system has helped police detect and locate shootings as they occur.

VentureBeat started writing about ShotSpotter back in 2006 and 2007. ShotSpotter’s website includes a Google map of installed sites.

ShotSpotter, Inc., headquartered in Mountain View, California — next door to East Palo Alto — was founded in 1996 and is funded by Band of Angels, City Light Capital, Claremont Creek Ventures, Labrador Ventures, Lauder Partners, Levensohn Venture Partners, Norwest Venture Partners and The Westley Group. The company has raised at least $20 million in funding.

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