Retardant drops are complicated

Several days ago, I was showing my nephew some pictures of tankers making retardant drops. He asked me how fast the retardant was falling when it came out of the tanker.

There is no simple answer to the speed at which the retardant drops out of the airplane onto the ground. The answer is, It depends. Some of you may recall that I wrote about retardant drops here, and information on retardant coverage levels from the USFS may be found here. The best drop is one that drops straight down as a heavy rain of retardant where all the retardant reaches the ground. In reality, this is hard to achieve, depending on a few different factors that all have to come together.

I'll start with the concept of the safe drop height. This is defined as the height above the ground that the tanker needs to fly in order for the retardant to drop straight down in a heavy rain of retardant where all forward momentum is lost. Drop to low and the forward momentum is not lost, resulting in possible injuries or even death to firefighters on the ground either from flying debris or from the retardant itself. Drop too high and the retardant disperses before it reaches the ground. To make it slightly more complicated the safe drop height varies depending on how much retardant is drop and the rate of flow from the tank.

How low are these tankers flying when they are making retardant drops? The multi-engine tankers are flying anywhere from 150 to 300 feet above the ground. Single-engine tankers are flying about 100 feet above ground level. This is dangerous flying, and the pilots know it. If something happens to the airplane when they are flying so low with a load of retardant (it is heavy), even the best and most experienced pilot may not be able to avoid a fatal crash.

Winds can affect the drop. A tanker pilot can take low winds into account when making the drop by either starting the drop before or after the start of the drop target depending on whether it is head or tail wind. But this only goes so far for sometimes the winds are too strong and dropping in conditions that are too windy can cause the retardant to miss the drop target. Sometimes the winds are too strong for the tankers to fly safely, not only will retardant drops in such conditions be ineffective, but strong winds can bring an airplane down.

Aircraft speed also affects the accuracy of the drop. The temperature and elevation affects aircraft performance which affects the accuracy of the drop.

What can I say to wrap this up? I'll quote one of my tanker pilot friends who keeps reminding me, "see I told you that the tanker business is complicated."

So, I think that the answer to my nephew's questions is, it depends because flying tankers is complicated.