CAT III Approaches

[RampFreeze]

All we need to do is get the powers that be to unleash the full capabilities of GPS LNAV/VNAV and stop worshipping at the altar of the antique ILS system

I couldn't agree with you more with respect to unleashing the full capabilities of LNAV/VNAV approaches. The USAF/military is way behind the civil sector with regard to heavy airplanes and instrument flying, specifically when it comes to the capabilities of FMS centered approaches. Every approach flown today by a USAF FMS-equipped airplane should be either an ILS or an LNAV/VNAV approach. (Course and glidepath guidance every time, regardless of the approach being flown, except a circle) The days of chasing a VOR, TACAN or NDB needle have gone by. Lateral guidance should be based on the LNAV magenta line from the nav solution exclusively (accurate to within a few yards) instead of a VOR or TACAN needle that can be +/- 4 degrees and up to 1/2 mile off for distance on a good day. (Yes, it is still a very good idea to cross check the raw data, but the primary guidance should be the magenta line instead of the other way around) This is the way any modern Boeing or Airbus is flown but does the USAF/AFFSA follow this logic - Nope. They would much rather have you chase an NDB arrow that points to the nearest thunderstorm and use the Nav Solution guidance as a "situational awareness" tool only. Come on AFFSA, lets get out of the stone age, the 757/767 has been flying this way since 1982!

Some think that the military is breaking trail with JPALS and some RNAV GPS approaches but unfortunately they have missed the boat entirely. The direction for airplanes with an FMS, a couple of INSs and GPS to go is RNAV RNP approaches and departures. Alaska Airlines has been doing this in 737s for 10 years now and many other airlines are also on board. When is the AMC/CC going to be briefed that there are public approaches (RNAV RNP) in the US that none of his airplanes can fly even though they offer tremendous operational gain? With RNP you can fly curved segments and get a lot closer to terrain than an RNAV GPS approach can. No ground NAVAIDs are required and it is the perfect solution to contingency ops when there is no ground infrastructure yet you need to fly in the weather to land at Base X. With all of the avionics mods being done in AMC are any of the airplanes terminal RNAV low-RNP certified? Nope - it is a crime. The closest they get are certification for RNAV GPS which is limited to straight line approaches with an RNP of 0.3NM.

As for the HUD, I still don't agree that you'll get any lower mins than you would with a heads down LNAV/VNAV approach. Would it be better to do it with a HUD? - absolutely. Unless you add EVS or some other synthetic technology I really don't see the minimums gain, with the exception of Cat IIIA hand-flown ops. Now if you are going to incorporate that (EVS, etc.) as well, it is an entirely different discussion. In any case, it is a good debate to be having...

I share your frustration with the USAF and its dependence on legacy ILS, TACAN, VOR and NDB. They simply don’t get it when it comes to LNAV/VNAV. One day they will advance beyond 1981 in both their policy and equipment.

 

[Gorilla]

You'll get no disagreement from me. While I no longer fly military, the mindset you describe is completely typical. RNP is the way to go.

The reason I advocate the HUD so strongly is two-fold. You are correct in that there is NO current, legal approach other than an ILS which gives the HUD-equipped aircraft any advantage. But there is definitely a dispatch advantage for HUD vs autoland, and the big issue in my mind is future operations. The HUD will allow display patching and modification to a greater degree than any heads down display.

In my B737 training, we did a half-dozen landings with no sim visuals at all, and I was very impressed by the ability of the hud to outline the runway to within a few feet. It was as if I was seeing the runway outline through some IR sensor, yet it was all derived from internal GPS data. I thought, "what a neat capability for the military. The HUD can 'draw' a runway, structure, taxiway, and I can land or negotiate that synthetic picture within a few feet." It's all about future capabilities.

Reliance upon ground-based navaids in this era of GPS/FMC is goofy.

 

[AdlerDriver]

Big difference between Cat IIIA and Cat IIIB (other than 400 RVR of vis required) is that Cat IIIB aircraft have 3 autopilots, etc that allow the system to be what is called "fail operational" where the loss of one system at the worst moment doesn't leave you hanging on one system that you "hope" is working correctly...

I don’t think the 3 autopilot requirement is exactly correct. That, I believe, is aircraft specific. The 757/767 had 3 autopilots for 3 axis control during auto-land ops as well as the “fail operational” criteria. However, the A-320 has two autopilots and is still Cat IIIB capable. With fly-by-wire, it doesn’t need 3 autopilots to get 3 axis control. The MD-11 also has just 2 autopilots.
All those aircraft get some level of “fail operational” status by various creative ways of isolating and/or splitting electrical sources for a long list of critical items. It’s been a while since I flew 757/767 – but my braincells still hanging on in the ICU remember something about using the APU (if available) for an extra level of redundancy on auto-land approaches. There was also some kind of electrical isolation that took place at 1500 or 1000’ (can’t remember). The A-320 does something similar. All this was a little less critical on the MD-11 due to the added redundancy of 3 engines/generators right off the bat.
Bottom line: I think the “fail operational” stuff is more dependant on how the aircraft protects and powers critical systems during auto-land than having 3 autopilots.

 

[RampFreeze]

I don’t think the 3 autopilot requirement is exactly correct

True, I was trying to keep things simple for the masses. The 757/767 has three flight control computers that feed into 3 autopilots. (another simplification, but close enough for government work) You are correct in stating that the Cat IIIB cert requirements vary based on system design.

 

[Big Beer Belly]

Reliance upon ground-based navaids in this era of GPS/FMC is goofy.

Ah .... so enjoyable to read intelligent discussion. I should stay away from the verbal "biatch slapping" on the major board more often!

Somewhat related, but perhaps not exactly on subject ... I thought I read (a while ago) that tests demonstrated that a puny 3-watt GPS jammer located near an airfield would render GPS-based autoland unacceptably inaccurate. 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? Bottom line in the article was the FAA was re-evaluating its previous decision to slowly decommission all ILS's (due to possible terrorist threat of jamming).

Anyone hear anything more on this?

BBB

 

[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