Low Power Surveillance Equipment for UAVs [UPDATE 3]

The FAA keeps harping on “Safety” and “Sense and Avoid” concerns when talking about integrating UAVs into the NAS. The AOPA has voiced similar concerns. There may be a simple way to answer some if not most of those concerns. (Updated)

UPDATED AGAIN: FAA Issues TSO-C199 for … essentially what we proposed here: Low Power Surveillance Equipment for UAVs.

From the C199 TSO:

The LPSE developed under this TSO is intended for use in aircraft that are exempted from carrying a transponder or ADS-B, such as gliders, balloons and aircraft without electrical systems, as defined in 14 CFR 91.215(b)(3), 14 CFR 91.215(b)(5), 14 CFR 91.225(e)(1), and 14 CFR 91.225(e)(2). The LPSE will allow these exempted aircraft to be seen by other aircraft equipped with: (TAS, TCAS, TCAS II) + …Aircraft with ADS-B In and display capability

The functional classes for this TSO are defined in Appendix 1 . These classes include: Class A, Low Power Surveillance Equipment, Class B, Low Power Surveillance Equipment with ADS-B Out, and Class C, Low Power Surveillance Equipment with ADS-B Out and ADS-B In.Class C is further subdivided into C1, 1090ES In, C2, UAT In, and C3, 1090ES In and UAT In



It is, of course, the most logical (obvious?) answer: A low power, short range, low altitude notification device for small UAVs that is compatible with the ADS-B system. Low power because the RPAs we are concerned about operate at low altitude and short range, with low power capability, which also avoids adding signal clutter to high altitude aircraft displays. I would further suggest that the low band – 975 mHZ – be utilized because the high band (1090 mHz) feeds a repeater system which extends the signal beyond the necessary range.

The FAA has set 2020 for the date that most all aircraft, including general aviation (private planes), should be equipped with ADS-B. The fact is that a large portion of aircraft flying today already have it, and the ground-based systems are set to be completed this year. As discussed in  the earlier post, ADS-B (Automatic Dependent Surveillance-Broadcast) is a system that tracks and broadcasts the position, altitude and speed (and thus the course) of an aircraft to other aircraft in the vicinity.

As expressed by the AOPA, pilots and operators of “manned”  aircraft are understandably fearful or concerned about remote controlled aircraft suddenly smashing through windscreens or being sucked into engines. Putting aside for the moment the fact that airlines and private pilots don’t normally fly below 400 feet AGL and that UAVs are prohibited above 400 feet, near airports or heliports, there is a pocket-size solution that can provide sense and avoid awareness for UAV pilots and spotters for less than $3.

FlightRadar24, available as a free app for Apple and some Android phones as well as versions for Mac and PC, provide a graphical display of aircraft in an area. The paid “pro” version also provides altitude and heading information. The $2.99 version showing altitude and course is the logical choice for UAV pilots and their spotters.

That takes care of ADS-B/in.

But let’s carry the discussion a bit further:

What is needed next is a new ADS-B/out standard for UAVs, including a Low Altitude/Low Power solution for smaller, short range, Very Low Altitude (VLA) craft.

The reason that a secondary LPLA ADS-B standard makes sense is a matter of numbers. It may seem like there are a lot of aircraft in the skies at any given moment but with thousands of RC “drones” being sold every month, just imagine if each one was also broadcasting ADS-B data over a wide area. That could result in a mass of signal clutter, with thousands of low altitude craft being mapped for short duration, much like watching pop corn pop. While it might be reasonable to require and equip larger (heavy) UAVs such as the civilian versions of the Puma and Global Hawk and even some larger RC models with ADS-B out due to their larger size and longer range capabilities, (and there is equipment available to do that), the altitude, short flight duration and smaller load capacity of smaller (light) unmanned aircraft make even the miniature standard ADS-B/out impractical. Besides the weight and size factor, the standard ADS-B/out transmits at 130 watts.

iphone2s[1]As discussed in the previous post the data necessary for ADS-B/out is being generated in the air for the Naza-M WooKong-M or Ace One flight controller by a UAV’s on-board GPS and compass.

That’s step one. That’s already available. (Thank you, Sagetech).

We mentioned that the standard ADS-B/out transmits 130 watts. That strong signal travels a long way. especially at high altitudes, much further than is necessary for the short (VLOS) range of a small UAV. That’s  overkill for a small quadcopter and requires too much power. A light (small) UAV only needs to announce its presence for a mile or two. The solution is a secondary low altitude/low power ADS-B/out specification standard for small UAVS, for a transmitter output of perhaps 100 mw.  Since ADS-B transmissions are in the form of data bursts (two per second), this solution is practical for the small UAV in several ways. The power required would not present a significant load to the UAV’s power system, perhaps reducing flying time by a minute or two at most. The altitude of the UAV increases the range of the transmitter to a mile or so, or just beyond the VLOS range of the UAV operator. That’s all we need. The UAV’s transmitter might use the 978 MHz (UAT) frequency designated for low altitudes rather than the 1090 Mhz (ES) used for higher altitude traffic displays..

That’s step two.

When it’s on the ground the signal from a low power transmitter doesn’t go very far, but it doesn’t need to. The computer in the standard ADS-B/in for full-size aircraft automatically detects and warns when another aircraft is on a collision course and ignores aircraft with a course that does not create a problem (behind, below or moving away). That’s what everybody wants.

A tiny, low power transmitter, weighing only a few ounces, similar to that used to send video to a ground controller, would connect to the GPS data port and power source in the UAV. Thus any ADS-B/in equipped aircraft in the local vicinity would be alerted to the presence of the UAV and warned if their courses intersect, and because of the smaller signal the main ADS-B system would not be overloaded with excess signals from dozens of small UAVs.

But there’s another minor stumbling block – According to my contact, Amit Regev, at Flytrex, DJI , unfortunately, does not use standard GPS formats, but their own generic serial protocol. There may be some people working on a way to parse out the data protocol from the DJI GPS. Considering the potential market for a ADS-B system for the large number of UAVs intended for commercial use, it might be in DJI’s interest to help facilitate a solution, if only for safety and insurance concerns.

All it would take to make it possible would be some technology cross-sharing between a company like Garmin or Sagetech, and DJI.  With the addition of Low Altitude Low Power (LALP) ADS-B, a local crop duster can be warned when approaching an sUAV and the sUAV operator or spotter can use a cell phone App (or eventually a remote controller alert signal as with low-battery warnings) to be aware of the approaching crop duster. The beach banner pilot and the real estate videographer shooting aerials at a condo will each be able to “sense and avoid” danger. The banner pilot would be alerted to the UAV and the UAV’s spotter, detecting an aircraft in the area, would simply send a warning (like the low battery warning) to the PIC (Pilot In Control) of the UAV to ground the UAV until the other aircraft has cleared the area. Under FAA rules (14 CFR 91-113), the aircraft that is less maneuverable has the right-of-way.
I recently enjoyed a conference call with the folks at Sagetech and I’m happy to say they at least didn’t dismiss the idea out of hand and could give it some consideration. Sagetech is a logical choice since they have already addressed ADS-B for heavy UAS with a tiny XP series transponders.

The low power on-board ADS-B/out for the small (light) UAV, with the convenience of a tablet or smart phone app for the UAV pilot and spotter can go a long way to solving the concerns about the safety of integrating small and large UAVs into the NAS (National Air Space). The miniature ADS-B out can be used for larger (heavy) UAVs.

An extra bonus could be gained if the sUAV ADS-B/out units could be designed to squawk a special UAV identifying code such as 9999. Larger UAVs could be given the option of dip switches for setting other 9000 transponder squawk-codes for FSS tracking. (A “default” code of 0000 indicates a manned aircraft with no active transponder)

The message to the FAA is this: provide for miniature ADS-B/out for UAVs 55 pounds and up and authorize a separate specification standard for low power/low altitude (LPLA) ADS-B/out for smaller UAVs for commercial use.  Light weight/low altitude UAVs should be made exempt from the FAA’s requirement for a IFR certified GPS receiver.

Some adjustment to CFR § 91.225 may be necessary providing for the low power/low altitude ADS-B/out transmitters and use of ADS-B/in by General Aviation and helicopters operating below 400 feet. That process can be completed in the space of a few weeks once the FAA is motivated. And with that problem addressed, we can finally proceed to commercial UAS licensing.

That’s step three. Simple, logical, practical and possible, right?

But is the FAA paying attention, or is their attention being misdirected by “other” forces and considerations?  There are indications that some DOD vendors (and their lobby) seems to be under the delusion that they could market $150,000 UAVs to farmers and charge $5,500 per hour as “consultants”.  The larger UAV community needs to find the means to counteract those influences.

Even in advance of full ADS-B implementation, the Sagetech device is available with Transponder Mode C and Mode S configurations.

Versions Available:

  • Mode C Transponder – Small, high reliability solution for Mode A and Mode C requirements (Mark XA AIMS certified version is also available)
  • Mode S Transponder with ADS-B Out – Enhance your safety of flight, thanks to increased visibility afforded by NextGen’s ADS-B
  • Mode S Transponder with ADS-B Out and GPS  – Include your GPS location in Mode S communications

RESOURCE/RELATED  2013 Study by Robert A. Klaus