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Using the C-39 Cockpit Indicator to Track Water Drops

Thursday, June 22, 2017

bambi bucket closeup

Over the past few years, governments have expressed a desire to know more details about the water that is dropped during firefighting efforts. This includes how much water is dropped, where it is picked up, and where it is dropped off.

C-39 Cockpit Indicator C-39 Cockpit Indicator
(P/N 210-095-00)

In March 2017, the US Forest service sent out solicitation RFP AG-024B-S-17-9002, which requires operators (in this case, Type II aircraft—mainly Medium Bell helicopters) to install an Additional Telemetry Unit (ATU) to:

Aircraft with buckets—especially those buckets without a pump—are required to use a load cell system to provide the information to the ATU. Onboard Weighing Systems include the C-39 cockpit indicator (to be replaced with the C-40 cockpit indicator), which already includes a 0-to-5 volt (V) Analog-Out signal that can be sent to the ATU. This signal can be used to detect changes to the weight on the hook (bucket fill and bucket open), as well as the weight of the water in the bucket.

Operators of the C-39 must access the SCALE function in the C-39’s menu to set up this system. The C-39 outputs a 0-to-5 V signal corresponding to the weight on the load cell, where 0V is 0 pounds/kilograms and the operator chooses the value of 5V in the SCALE menu. The 5V signal should be set to near the maximum external load capacity of the helicopter, or slightly more. For example, if the maximum load a helicopter can lift is 4,000 pounds, the 5V signal could be set to 4,000 pounds. However, if more than 4,000 pounds was accidentally picked up, the C-39 would only output the same 5V, so by setting the 5V signal to 5,000 pounds, it would provide details on how much extra weight was lifted.

Finally, the C-39’s analog output signal would need to be wired to some data collection instrument, such as those from Latitude Technologies or FlightCell. The weight information from the C-39 could then be joined to the GPS & Flight information, and then sent to the Automated Flight Following (AFF) system for transmission to the Forest Service. The C-40 Cockpit Indicator will have ability to perform many of these data collections functions when it becomes available.

Tags: cockpit indicator, usfs, us forest service (usfs), additional telemetry unit, atu, analog-out signal, data collection