Faulty Foam System Fills Hangar


Airlive is reporting that at least three aircraft were damaged when a malfunctioning foam fire suppression system filled a hangar in Texas. According to the time stamp on the surveillance video, the mishap happened on Oct. 28 at McKinney National Airport likely just before noon. It’s not clear what triggered the foam, but it’s most commonly referred to as an equipment problem and not human error.

The time lapse of the video shows about 10 minutes of the incident and in that time foam fills the hangar up to the windows of a business jet. Airlive says the foam is corrosive. Technical websites say the planes have to be thoroughly rinsed and then inspected for damage before being put back into service. It’s not clear who owned the planes.

Russ Niles
Russ Niles is Editor-in-Chief of AVweb. He has been a pilot for 30 years and joined AVweb 22 years ago. He and his wife Marni live in southern British Columbia where they also operate a small winery.


  1. Saw this happen by accident in a large, brand new, still-empty corporate hangar big enough to hold multiple Bombardier GEs. Doors closed automatically, and a crowd of us stood open-mouthed watching the foam come out of vents at the *top* of the hangar walls like somebody put too much of the wrong soap in their laundromat front loader.

  2. No mention of the danger posed to anybody working in the hangar. Designed to quickly fill the hangar with foam within minutes, they can be dangerous to personnel–it doesn’t take long to put down a life-snuffing 5-6 feet of foam.

  3. It seems to me there have been more aircraft damaged by inadvertent foam activation than actual hangar fires….

    • The Air Force had one discharge up in Minot, North Dakota, in a hangar with a couple B1 bombers inside. By the time they got it shut down, foam had virtually covered the planes. Considering the special radar absorbing paint on the B1, I suspect that was a very expensive cleanup. And yes, accidental discharges happen far more often than in an actual fire. That’s why training of personnel in what to do is so important.

  4. Over my career, I had the opportunity to help design and test a few of these high-ex foam systems in large hangars. The automatic systems are equipped with an alarm and time delay circuit that allows (usually) 30-60 seconds before the main foam discharge begins. In that time, someone familiar with the system can investigate and press a switch to prevent accidental discharge. Usually this switch does not abort a discharge, but will reset the delay switch giving people additional time to either investigate or evacuate. Once activated, they are designed to completely cover the floor surface of the hangar with 3 to 6 feet of foam in about 90 seconds – usually plenty of time for anyone in the hangar to evacuate. The foam is not hazardous to personnel, but will make the floor quite slippery, so falls are a definite hazard. Once the system is running, the foam chambers are powered by water pressure, meaning no electrical power is needed. The water pumps are normally diesel engines that will also run with no external power. So, once the system is activated, the only way to stop it is to manually shut down the fire pumps, which are usually in a room in the building or a separate building close by. Depending on the design, the systems can activate by a signal from an optical “fire eye” detector that “sees” a flame, or by a manual button generally located by the exit doors in the hangar. The optical detectors can sometimes be tricked by seeing a welding spark, lightning outside the building, or sometimes reflected sunlight off a shiny floor surface. The newer detectors are much better at ignoring those signals, but standard procedure should be to disable them whenever there is hot work in the hangar or lightning storms outside. A good system also has covers over the manual buttons to prevent accidental contact. One of my clients dumped their system when a janitor’s mop handle fell against an uncovered button.

    With this accident, since it happened during normal work hours, there was almost certainly someone in the building that could have prevented the discharge or minimized the damage. However, that would require knowledge of the system and what to do. We always insisted on training the client’s employees in how the system worked and what to do if the alarm went off. As the article said, the foam is corrosive, but can be easily cleaned off if washed down before it dries. But cleaning up the planes will be important, time consuming and expensive. Also replacing the foam supply will be costly, as most systems carry about 1,000 gallons of concentrate, costing around $40 dollars a gallon.

  5. “Depending on the design, the systems can activate by a signal from an optical “fire eye” detector that “sees” a flame, or by a manual button generally located by the exit doors in the hangar. The optical detectors can sometimes be tricked by seeing a welding spa”.

    Good to know–but as someone that has had several false “fire eye” detectors causing the Engine Fire Light to illuminate in older King Airs over the years–that would give me cause for ADDITIONAL worry. The photocells detect flickering sunlight as “fire”. The first thing they teach in King Air school on these airplanes is “turn away from the sun” in the event of a fire light. According to King Air magazine author and lecturer Tom Clements, there has never been an actual engine fire in these older King Airs–though there have been SO MANY FALSE ALARMS. There HAS to be a better and safer way!

  6. Perhaps right now someone is developing an AI model to watch video camera feeds and detect a fire better than any previous sensor-based methods. Look for a release of such tech within 12 months.

  7. The technology behind the fire eye detectors has evolved a lot in the past decade or so. The original detectors simply reacted to a certain spectrum of UV light, know to be present in hydrocarbon fires. Unfortunately, it also appears in the other false signals. I suspect the units in the old King Air systems were the single-spectrum models, considering the time they were in service. The new multi-spectrum units can filter out welding and lightning quite well, but still not perfect. A well designed system will require cross zoning or multiple detectors before an actual discharge occurs. Perhaps AI might help, but it would still have to rely on some optical sensor to decide what is actually happening. That is why we stressed training and how to delay activation with our clients. But, an errant mop handle is hard to defeat! We also had another system trip when a maintenance worker replacing a defective detector managed to stick his screwdriver in the wrong place and short out the wires. He should have shut down the system first, but was in a hurry. Oops, did I do that?