CO737 From United States of America, joined Dec 2000, 146 posts, RR: 0
Reply 1, posted (10 years 9 months 3 weeks 5 days 12 hours ago) and read 5018 times:
Catergories refer to the minimums for the ILS. CAT I are your standard minimums (200 ft. AGL and 1 mile visibility). CAT II have lower minimums (100 and 1/2, I believe). CAT III don't have a ceiling requirement, but are based on the runway visual range. Any instrument rated pilot can shoot a CAT I, but CAT II and III approaches require special training and aircraft equipment.
RVR is Runway Visual Range, basically a distance in feet that the pilot can expect to see forward in his airplane.
The ILS equipment at the airport must be certified for it, as well as aircraft type (actually individual aircraft) and crew have to be certified.
Alert Height (AH) is not like a Decision Height (DH) -
At "DH" (obtained from radio altimeter for Cat.II) you have to make a DECISION to land or go-around...
In Cat.III operations, there is no DH... but you have to make a decision to land based on "what you see"... pilots find the DH "decision" very convenient for Cat.II, but did not exist for Cat.III...
So in "pratical operations", the AH is used somewhat like a DH, but is not regulatory. In other terms, we expect to "see the runway" at that point... which is about 50 feet radio altimeter, just about where the runway threshold is located, in Cat.IIIa minimums. In Cat.IIIb, happens at about 35 feet...
Many 747 are equipped for Cat.IIIa operations (not Cat.IIIb), although most of the "Classic" 747s (with 3 autopilot channels) have the LRCU that is required for Cat.IIIb... LRCU = landing roll control unit... keeps the nose wheel on the center line, using the localizer...
"There are no stupid questions, but there are a lot of inquisitive idiots."
PhilSquares From , joined Dec 1969, posts, RR:
Reply 3, posted (10 years 9 months 3 weeks 5 days 9 hours ago) and read 4917 times:
Quoting Starlionblue (Reply 2): Many 747 are equipped for Cat.IIIa operations (not Cat.IIIb), although most of the "Classic" 747s (with 3 autopilot channels) have the LRCU that is required for Cat.IIIb... LRCU = landing roll control unit... keeps the nose wheel on the center line, using the localizer.
All the -400s come from Boeing with the capability for CAT IIIC. The operator's ops specs might not be for CATIIIC but for a lower category. That lower category would then become limiting factor.
For example at SQ, we are CATIIIB with an alert height of 20'.
Boeing7E7 From , joined Dec 1969, posts, RR:
Reply 4, posted (10 years 9 months 3 weeks 5 days 9 hours ago) and read 4906 times:
CAT I/II - ILS, Terrain, Aircraft Equipment, Approach Lights and Crew based minima.
CAT II is nothing more than a CAT II with additional pilot qualifications.
Explaining TERPS is a real pain in that I can't send you to a direct document as the FAA has seen fit not to make all of the publications available to the general public. If you ask a FSDO they may provide you with a copy of the TERPS manual the FAA uses to define approach minima, slopes and system criteria.
There are about 8 components that make up the TERPS standard which enables the Category of ILS approach. For example. CAT I/II only requires ALSF-I approach lights, CAT II/III is ALSF-2. A simple variation in the airfield altitude changes the dynamics of the approach surface exponentially.
Here's a link where you can get some very basic info on TERPS. The basic document is the 8260, but it's not all there. It's as if they don't want some farmer with a landing strip is goign to go out and trying to get his own CAT III approach or something:
Boeing7E7 From , joined Dec 1969, posts, RR:
Reply 9, posted (10 years 9 months 3 weeks 4 days 18 hours ago) and read 4740 times:
I should also add that the US just shit canned another landing system LAAS for the short term. After wasting 7 years with Raytheon and 2 years with Honeywell they magically discovered that LAAS as envisioned would not provide CAT III capability. Nice. Real nice. MLS anyone???? AGAIN!!!!!!!!!!!
Although with MMR's, FMS, WAAS, IRS/INS and MLS accuracy.... Imagine the possibilities.... Hello FAA... Anyone listening?????
Saab2000 From Switzerland, joined Jun 2001, 1621 posts, RR: 11
Reply 11, posted (10 years 9 months 3 weeks 4 days 14 hours ago) and read 4678 times:
When I flew Saab 2000s in Europe, we were certified to CAT IIIa minimas. It was handflown with a HUD - Head Up Display. If the flying pilot (always the captain in the case of the Saab 2000) deviated enough, it caused a "Loss of Approach" warning and a go-around was required.
It was a fairly simple operation to be honest, and we never had to go around.
I cannot speak of other categories of approaches, but the CAT IIIa approaches on the Saab2000 are hand flown.