Monday, June 16, 2014


Wow, I can't believe I haven't written this post yet. I have mentioned RAIM in other posts, but I haven't explicitly explained RAIM. RAIM used to mean Redundant Autonomous Integrity Monitoring it was a technology built into many GPS receivers. TSO-C129 required GPS receivers to have RAIM built in. It would monitor the quality of the GPS signal, and if things were bad enough, the RAIM system would alert the pilot that things aren't working.

If you go back to the NextGen post I did a little more than a year ago, I mentioned RAIM, and the FAA's RAIM prediction tool: this tool will predict places in the CONUS where the RAIM alert will go off in the future.

The GPS signal is just telling you what the time was when the satellite sent the signal. The satellites also send location information along with the time. The almanac is the location of all the satellites in the constellation. Knowing the time the satellite sent it's signal, and knowing where the satellite was when the signal was sent, the GPS receivers are able to triangulate (sphere-iate?) their location.

The satellite time message is sent every few minutes, and is susceptible to all kinds of problems. The message may bounce off buildings, mountains or other vehicles causing a wrong distance to be calculated. Other times the satellites will be down for maintenance, and testing, so it won't be available for measurements. Knowing the current status of the constellation is critical to make a valid prediction. Knowing local terrain will help make predictions more accurate.

With GPS Helpers, RAIM prediction is not needed. Using satellite or ground based augmentation systems (IE WAAS, LAAS) the number of satellites isn't as critical. Knowing the WAAS system health is required, and the FAA will issue NOTAMs if the WAAS system isn't up to snuff.

As you can see RAIM has its use, and can make older GPSs more usable.

Saturday, June 7, 2014


The FAA has a huge challenge, they need to get it right the first time. If they screw it up, and a UAS and a passenger aircraft have an issue, where people get hurt, there will be no more UAS allowed! Of course, the UAS industries are clamoring for changes now. Claims of huge employment are dubious, since it will only transition pilots and maintenance from manned aircraft to unmanned (peopled, what is the right non-gender word).

If people think everything under 400ft (1000ft, 2000ft, whatever) should be unregulated, what happens when a traffic accident occurs, and a medical helicopter has to thread it’s way through 5 local TV stations with their quad copters filming the carnage? What are the rules around an airport? The rules have to at least match the controlled/uncontrolled/class A/B/C/D rules that exist for manned aircraft. Rules need to be established, such that assistance cannot be delayed.

Quad copters and other UAS devices are easy to fly when the weather is nice and there is little wind and turbulence. What happens when there is turbulence, or dust or other weather that makes visual queues, and control difficult. How about a slightly damaged older device that isn’t well maintained, and the operator is inexperienced. The innocent people on the sidewalk should expect a reasonable amount of safety near these devices.

Many of the smaller quad-copters are only controllable indoors, and some of the larger ones are controllable in moderate winds. Larger UAS systems are less prone to weather, but are more dangerous to people around them. What happens when an editor or producer is clamoring for a news story on a stormy day? What is the poor UAS operator to do, fly anyway? The operators will be glad to have an FAA regulation that says it isn't safe, so they won't have to stress about it.

There will need to be right of way rules. Right of way rules make knowing what to expect from the other aircraft. It is all great to have see and avoid, but what is the understood direction to avoid things? Most R/C fliers operate with one aircraft in the pattern at a time, so they don't have too many right of way issues. Much of this will be new territory to UAS operators.

For commercial UAS operators, there will need to be maintenance programs designed. Basic maintenance will need to be regulated to insure the craft is controllable, as well as structurally sound. Having a UAS disassemble in flight will make the situation for the operator inconvenient. Inspections, and preventative maintenance programs will have to be defined. 

There will be all kinds of other regulations that most people haven’t considered.
Pilot licensing being one. If a UAS is to be operated in the same airspace as a manned system, the operator MUST know the same rules as the manned aircraft, at least to know what everyone will expect in right of way situations. 

The FAA could mess all this up and not regulate it properly, and people will get hurt. The FAA is already granting exceptions for certain groups, but this sets a bad precedence. They could rush, or some manufacturer could lobby congress to get the FAA out of the way, and people would get hurt. If a UAS took down a 737 you will see congress act!

Everyone needs to be a little more patient, and let the process work it’s way out.