CAT III Approaches

[HoursHore]

The USAF/military is way behind the civil sector with regard to heavy airplanes and instrument flying

Remember, your talking about the Air Force.

Old guys in my squadron are having conniptions about training new pilots to fly in both seats. Hell, they still don't believe in checklist flows either.

 

[RampFreeze]

My understanding was that a "corrected" GPS signal from a local transmitter was required to obtain the necessary autoland accuracy. Has this been altered since the DOD removed the accuracy "skewing" (not sure its technical name?) algorithm from the satellite signals?

LAAS stands for Local Area Augmentation System and is a local, ground based transmitter that provides the "correction" to the GPS signal you were describing. Yes, it is still required even with Selective Availability (the intentional "skewing" you describe) turned off. Boeing has been doing some work with LAAS and has been having some incredibly impressive results with Cat III autolands using a LAAS system. Unfortunately, the FAA has been dumping its resources into WAAS instead. There are benefits to the aviation community as a whole with WAAS for sure. However, LAAS offers a lot more promise IMHO.

As for the GPS jamming. I can't speak to it other than to say yes, you can jam the signal. I'll also say that for every problem there usually is a remedy. I honestly don't think it is of grave concern to the extent that it is slowing down LAAS development. Everything I have heard states that the ability to jam a GPS signal is not what is holding back faster LAAS development, a lack of $$$ from the FAA is the problem. Right now they are spending the money on WAAS.

 

[Big Beer Belly]

LAAS stands for Local Area Augmentation System and is a local, ground based transmitter that provides the "correction" to the GPS signal you were describing. Yes, it is still required even with Selective Availability (the intentional "skewing" you describe) turned off. Boeing has been doing some work with LAAS and has been having some incredibly impressive results with Cat III autolands using a LAAS system. Unfortunately, the FAA has been dumping its resources into WAAS instead. There are benefits to the aviation community as a whole with WAAS for sure. However, LAAS offers a lot more promise IMHO.

As for the GPS jamming. I can't speak to it other than to say yes, you can jam the signal. I'll also say that for every problem there usually is a remedy. I honestly don't think it is of grave concern to the extent that it is slowing down LAAS development. Everything I have heard states that the ability to jam a GPS signal is not what is holding back faster LAAS development, a lack of $$$ from the FAA is the problem. Right now they are spending the money on WAAS.

Thanks for the update Ramp!

It's funny the pecking order of technology sometimes. The military guys moan they are in the dark ages compared to 121 and the 121 folks scream we are decades behind the corporate jet guys. Finally, my employer has decided to embrace technology in the cockpit by installing Class 3 Electronic Flight Bags (starting with the 757/767's ... the 747-400's and A-380's will come factory equipped with them.) Runway incursions should be a thing of the past with moving map airport diagrams and real time data-linked weather over the entire route of flight should save fuel by avoiding the "drive up to the cell, big last-minute deviation around" maneuver we currently do.

BBB

 

[Gorilla]

GPS jamming! Ouch, good point, I never thought of the possibility of intentional interference.

I would suspect that any aircraft designed or certified for some future, super-RNP approach would have to be pretty bulletproof. FMC software would have to monitor the GPS signal to detect jamming or tampering, and rely on the IRU's to help validate. Any issues in the critical regime of 0' to 200' = automatic go-around.

The GPS system is simply amazing. It irritates me a bit that the U.S. taxpayers paid for this phenomenal system, yet everyone worldwide gets to use it. For good or ill... a primitive but accurate cruise missile can be made out of a small general aviation aircraft with GPS, a good autopilot, and packed with Semtex.

I'll bet a beer that somewhere in the bowels of NORAD is a red guarded switch labeled GPS ENCRYPT that commands the satellites to scramble their signal, leaving only U.S. military GPS recievers functional. Any takers?

:beer:

 

[Big Beer Belly]

GPS jamming! Ouch, good point, I never thought of the possibility of intentional interference.

The GPS system is simply amazing. It irritates me a bit that the U.S. taxpayers paid for this phenomenal system, yet everyone worldwide gets to use it. For good or ill... a primitive but accurate cruise missile can be made out of a small general aviation aircraft with GPS, a good autopilot, and packed with Semtex.

I'll bet a beer that somewhere in the bowels of NORAD is a red guarded switch labeled GPS ENCRYPT that commands the satellites to scramble their signal, leaving only U.S. military GPS recievers functional. Any takers?

:beer:

It's the double-edge sword or law of unintended consequences or whatever the cliche is. Fact is the same great GPS system the US uses to guide munitions is also the one the enemy will use to guide its munitions back at us. Our scientists have expended an extraordinary amount of money and brain cells on developing autonomously guided, highly accurate ICBM's and other weapons which require no external data input to hit their target. An unfortunate consequence of GPS is that it now provides nearly identical precision very inexpensively to our foes. Old Soviet-era inaccurate missiles are now very accurate and very cheap to retrofit with GPS receivers. Thus, previous third-world thugs with access to old missiles now pose a significant threat (i.e., Iran, Syria, N. Korea ... hmm, where have we heard those before?)

I do know the US has the capability to turn the GPS signal "off" any or all of the satellites, but so much of our combat strategy (both land and air) relies on these satellites that it is questionable if that would occur.

Another very serious concern is the ability of our foes to destroy the satellites and our ability to defend them. This "basic" concern has been "considered" by many very intelligent people for a long time. I'm confident a solution has been found.

BBB

 

[airgator]

After further review...

I found out despite the fact the AMP planes are capable of CAT III's, we are not allowed to do them. I have a feeling when they start putting the new engines on and finish the various other upgrades in the next couple years we will be CAT III certified.

 

[RampFreeze]

I found out despite the fact the AMP planes are capable of CAT III's, we are not allowed to do them. I have a feeling when they start putting the new engines on and finish the various other upgrades in the next couple years we will be CAT III certified.

I'd always been told that the original flight director, autopilot, et al. on the C-5 was Cat III capable. (i.e. that's why it had/has the funky ADI that spun around when in ILS approach mode and illuminated with the amber ring at mins and green circle when flare mode engaged) Even though the original system was Cat III capable MAC/AMC never wanted to pay the $$$ to maintain it fleet wide and was happy just maintaining Cat II capability. It wouldn't surprise me if they applied the same logic to the AMP, etc. project. Time will tell...

I would suspect that any aircraft designed or certified for some future, super-RNP approach would have to be pretty bulletproof. FMC software would have to monitor the GPS signal to detect jamming or tampering, and rely on the IRU's to help validate. Any issues in the critical regime of 0' to 200' = automatic go-around.

I don't think it would have to be that comic at all. It would be like any current RNP approach. If the FMS detects an unusual disparity between GPS position and other nav inputs (IRU, DME, VOR, LOC) it increases the ANP (Actual Nav Performance) circular probability of error. If this value exceeds the RNP (Required Nav Performance) value, an "UNABLE RNP" alert is issued and, just like today, regardless of where you are on the approach, you have to go around unless you see the runway. With a LAAS Cat III system, my guess is that if the box lost the correction signal from the LAAS unit for any reason (jamming or just simple failure) the same alert would be issued and a go-around would be initiated. So, I go back to my original position - I don't think LAAS is being fielded yet because of an FAA $$$/funding priority issue. I honestly don't think the security issue is that much of a concern.