Please explain Cat I and Cat II terms

[El Cid Av8or]

Something I have always wondered but never could find a good definition for (I haven't really looked that hard yet) was the meaning of Category I and Category II aircraft. While we're on a related subject, what weight constitutes a "heavy" aircraft? I am referring to a situation like the phrase "Delta 99 Heavy, cleared to land runway 33, winds..."

Ya'll have a good day...

 

[flywithruss]

An aircraft is classified as "heavy" if it has a maximum gross takeoff weight (MGTOW) in excess of 255,000 pounds. Basically, this consitutes the B757 and widebody airliners.

Heavy aircraft require greater separation on departure and arrival for wake turbulence avoidance than do smaller aircraft.

R

 

[metrofo]

Well ElCid, there is actually a CAT I, CAT II AND CAT III category of aircraft and even more clasifications withing the CAT III level. All of these refer mainly to the aircrafts certified weather landing minimums. Most commercial aircraft are CAT III but as a practical matter in the US, CAT II is probably the lowest landing weather mins you will be authorized. Some places overseas have CAT III landing mins down to as low as 600 RVR (commercial aircraft, military can be even lower). Basically most CAT I landing mins will go to as low as 1/2 mile vis or 1800 RVR if that is reported. Most CAT II mins will be 1200 RVR as RVR is required for anything below a CAT I approach. One more mention, the crew must be specifically trained on low vis approaches in order for the approach to commence beyond the normal CAT I mins of 1800 RVR.

 

[El Cid Av8or]

Thanks!

flywithruss & metrofo:

Thanks for the excellent explanations. I didn't sleep at a Holiday Inn Express last night so you both have been very helpful.

Isn't there a Cat I, II (and probably III) noise level certification too? I thought I read something about Cat II jet aircraft not being allowed at certain airports (at least the local community was pushing it really hard) after hours due to the excess noise from the engines. Or would this be because of the instrument approach path?

Also, I am guessing that the "CAT I" & "CAT II" etc. signs on the runways have something to do with the weather category certification for takeoffs and landings?

At any rate, if anyone wants to give free classes on using the HUD in the G-V or Falcon 900EX, I'm game

 

[TriDriver]

Cat II/III

El Cid

I'm not looking at approach charts or ops specs right now, but:

Cat I is what you regularly fly on an ILS when you go down to 1/2 mile vis or 2400 (sometimes down to 1800 foot) RVR, and is usually a 200 foot Decision Altitude/Height. These are the regular appch chart minima you normally see when you look at an ILS appch chart.

If you look at a Cat II/III chart, it looks about the same except it says something like "special aircraft and crew certification required" and the minimums are based on RVR and radio altitudes. At the airlines, we practice in the sim and get certified down to the lower minima of these approaches. They are generally required to be flown by the captain only, and our scan policy is different, i.e., down toward mins, the captain is not looking inside at all - he in only looking out, and he is the pilot that will call the approach lights/runway environment in sight. The first officer is monitoring the guages and making sure the autopilot is doing its thing.

Typically a Cat II appch will get you down to either a 150 ft decision height/altitude with a 1600 ft RVR, or a 100 ft DH with 1200 or 1000 RVR. On the 737 I fly, we can only go to 150 DH if only one autopilot is working, and we must use the flight directors. If both autopilots are working, we can go to 100 DH and 1200 RVR. If we do an autoland, we can go to 1000 RVR.

For Cat III, we have to do an autoland. We go to 50 foot DH and need 600 foot RVR. Both autopilots, both flight directors, the autothrottles, and radio altimeters have to be working, along with all the airport related stuff such as approach light system, touchdown zone lights, center line lights, etc. A lot of the real low vis airports also publish a SMGCS chart which is a low vis taxi chart, and they have to have special taxiway lighting installed. Obviously not all airports and runways have all that.

For both of these lower vis approaches, there is a lot of ground and aircraft stuff that has to be installed and working. On the 727, the lowest we could go was Cat II (no autothrottles or autoland capability). Some aircraft may be able to do a hand flown Cat III (I'm not sure, but if they are allowed to, it would probably require a Heads Up Display system). I know some aircraft are approved down to 50 foot Alert Height and 300 foot RVR vis. The Alert Height is not even a Decision Height/Altitude, because you don't even have to see anything at that point - all you have to do is be assured everything is working okay, and you let the aircraft go on down and autoland itself.

The hardest part of a real low vis approach is trying to taxi in and find your gate!

TriDriver Bob

 

[metrofo]

Hello again EL Cid,
The noise requirments you are referring to are STAGE II, III and IV. These can be found and researched by looking under FAR part 36 which governs noise compliance of aicraft and specific airports. The higher the stage number, the lower the noise signature for that aircraft. In the coming years, more and more aircraft will be required to be quieter in order to operate at certain airports and certain times. Most modern a/c can meet the latest STAGE III noise requirements without any modification. Some aircraft, need to have hush-kits installed on the engines to lower the noise signature to allow them to comply with these restrictions.

 

[El Cid Av8or]

Outstanding!!!

Thanks once again, folks!!!

I think I'll stay with the Cat I stuff for a while. This one really made my day..."The hardest part of a real low vis approach is trying to taxi in and find your gate!" Now that's a good one! I guess it's one of those really slow taxis and you hope that the airport designers were nice enough to put the cool taxiway centerline lights on the plans.

Thanks once again for the help...on STAGE 1,2,3 noise requirements too.

 

[501261]

Re: Thanks!

flywithruss & metrofo:

Isn't there a Cat I, II (and probably III) noise level certification too? I thought I read something about Cat II jet aircraft not being allowed at certain airports (at least the local community was pushing it really hard) after hours due to the excess noise from the engines. Or would this be because of the instrument approach path?

Also, I am guessing that the "CAT I" & "CAT II" etc. signs on the runways have something to do with the weather category certification for takeoffs and landings?

ElCid, what you're thinking of is STAGE I, II, and III noise limits. This is on a jet's design certification. Most jets that are out flying today meet the Stage III requirements. Some older planes still flying that are Stage II are old Lear 23, 24, 25's, 727's, etc. Basically the old loud stuff. Even louder than Stage II is Stage I, the only airplanes that I can think of that are certified Stage I are Jet Commanders and old Jet Star's (not re-engined).

A lot of airports in noise sensitive areas (read California or Europe) will not let Stage II aircraft in. Europe was even talking about developing a Stage IV standard that would be quieter than Stage III.

Tridriver hit the Different approach Categories very eloquently.

There is another Category for airplanes and that is Air Traffic Control Classes; Heavy (above 255,000lb), Large (254,000-41,000 lb.) Small (less than 41,000). Different Classes have different wake turbulence separation minima. Incidentally the Falcon 900 is large at 46000lb.

 

[bigsky]

In reference to heavey, I dont believe the 757 was classified as a heavey until the 757-300 actually exceeded the 255,000 cutoff. They do produce nasty wake vortices so they had their own in trail seperation minima.
For example large aircraft are required to be 2 min and 5 miles behind heavey and 2 minutes and 4 miles behind a 757.

 

[AAflyer]

The 757 at AA is certified at 241,000Lbs for the domestic birds, and 251,000 for our ER birds. They are not considered heavy.I believe UAL,NWA,DAL have similiar weights all below 255K as I have never been instructed to follow the heavy United 757 on short final.

I believe ATA has 757-200s (and 300s which are heavy) that are also classified as heavy. The engines (RB-211s) put out 43,100Lbs of thrust, and could easily accomdate weights in excess of 255,000. My understanding is this is a certification process (that term is synonomis with cash and FAA).

As for nasty wake turbulence, not so, the 757 is able to descend at steeper angles on approaches, which can cause other aircraft a bumpy ride when they fly through it. According to boeing people the 757 wake is no worse than any other.

AAflyer

 

[chperplt]

As for nasty wake turbulence, not so, the 757 is able to descend at steeper angles on approaches, which can cause other aircraft a bumpy ride when they fly through it. According to boeing people the 757 wake is no worse than any other.

Well, from my experience, I've had more "fun rides" behind the 757 than any other airplane.. I posted about a wake turb encounter I had in LGA last week. 4.5 miles behind and a dot high on the approach and got rocked.

 

[TriStar_drvr]

I know that ATA's 757-200s are certified for takeoffs over 255,000 pounds. It's not much over, but just enough for the pilots to get to call themselves a heavy. I guess with the -300s there is no question.

I'll try to find out the exact number from one of our 757 pilots.

 

[501261]

Of course Boeing tells you that the 75 has no wake turbulence. I once had a Boeing salesman tell me that the -300 would also have no problems with tail strikes.

No, 75's produce some bad turbulence. Seems like the vortices are small, yet very powerful. Unlike the heavies (74's, 77's) that leave a large area of disturbed air. The 75 will definitely "rock" you! I've never been "rocked" by a 737 or MD-80 or A320, also never been really “rocked" by a heavy either because of the separation requirement. But I've definitely been "rocked" on a few occasions by 75's.

Another airplane that'll rock you is the 727's, I think they're almost as bad as the 75's, but no one talks about them!

 

[cvsfly]

I believe some years ago the B-757 was put into a special category because its wake signature was found to be more like the heavies. It is not called a heavy as far as aircraft certification goes, but with respect to ATC separation I believe it is treated like a heavy. See AIM 7-3-9.

 

[AAflyer]

Well considering I fly it, I would have to say that the ATC seperation being the same as a heavy is a total BS. I have never been held for two minutes while a 757 departs, or been given an intrail speration for a 757.

As for not being rocked behind a A320, I certainly have and would not have been able to tell the difference between the two.

Last but not least. I am not sure who at Boeing you spoke with, but AA was informed of the possiblity of tail-strikes on the -300, and it impacted the decision not buy them, due to the runways and high altitudes in central and south amercian airports.

AAflyer

 

[cvsfly]

I don't care what you you fly. I gave the reference, so read it.

7-3-9. Air Traffic Wake Turbulence Separations

a. Because of the possible effects of wake turbulence, controllers are required to apply no less than specified minimum separation for aircraft operating behind a heavy jet and, in certain instances, behind large nonheavy aircraft (i.e., B757 aircraft).

1. Separation is applied to aircraft operating directly behind a heavy/B757 jet at the same altitude or less than 1,000 feet below:

(a) Heavy jet behind heavy jet-4 miles.

(b) Large/heavy behind B757 - 4 miles.

(c) Small behind B757 - 5 miles.

(d) Small/large aircraft behind heavy jet - 5 miles.

2. Also, separation, measured at the time the preceding aircraft is over the landing threshold, is provided to small aircraft:

(a) Small aircraft landing behind heavy jet - 6 miles.

(b) Small aircraft landing behind B757 - 5 miles.

(c) Small aircraft landing behind large aircraft- 4 miles.

REFERENCE-
Pilot/Controller Glossary Term- Aircraft Classes.

3. Additionally, appropriate time or distance intervals are provided to departing aircraft:

(a) Two minutes or the appropriate 4 or 5 mile radar separation when takeoff behind a heavy/B757 jet will be:

(1) From the same threshold.

(2) On a crossing runway and projected flight paths will cross.

(3) From the threshold of a parallel runway when staggered ahead of that of the adjacent runway by less than 500 feet and when the runways are separated by less than 2,500 feet.

NOTE-
Controllers may not reduce or waive these intervals.

b. A 3-minute interval will be provided when a small aircraft will takeoff:

1. From an intersection on the same runway (same or opposite direction) behind a departing large aircraft,

2. In the opposite direction on the same runway behind a large aircraft takeoff or low/missed approach.

NOTE-
This 3-minute interval may be waived upon specific pilot request.

c. A 3-minute interval will be provided for all aircraft taking off when the operations are as described in subparagraph b1 and 2 above, the preceding aircraft is a heavy/B757 jet, and the operations are on either the same runway or parallel runways separated by less than 2,500 feet. Controllers may not reduce or waive this interval.

d. Pilots may request additional separation i.e., 2 minutes instead of 4 or 5 miles for wake turbulence avoidance. This request should be made as soon as practical on ground control and at least before taxiing onto the runway.

NOTE-
14 CFR Section 91.3(a) states: "The pilot-in-command of an aircraft is directly responsible for and is the final authority as to the operation of that aircraft."

e. Controllers may anticipate separation and need not withhold a takeoff clearance for an aircraft departing behind a large/heavy aircraft if there is reasonable assurance the required separation will exist when the departing aircraft starts takeoff roll.

 

[bigsky]

I believe the 757-300 is around 272,000 at mtow.

 

[501261]

CVSFLY, thanks for the reference. I did not realize that the separation was based on when you're crossing the threshold. That makes sense to me now. Seems like every time I've been "rocked" by a 75 is when a controller gave me an early turn into the approach, followed by "slow to final approach speed." In essence turning me when I'm only 4 miles in trail of the 75, but slowing me so that I would have 5 miles by the time I crossed the threshold.

 

[AAflyer]

CVSFly,

I read your post, and the AIM section, you are right. Which then caused me to wonder why in certain cases this is not applied. I should say more than certain cases. I see it violated alot. I will pay closer attention to it now to see. So I did some research.

I did find a bulletin called ANTICIPATED SEPERATION at

www.faa.gov/ATPubs/ATB/atbhme.HTM

It is under the above named title. dated 00-6 FALL 2000

All I can figure from this is that it is not being followed and maybe they need to be called on it.

 

[cvsfly]

Back to the terminology here. I recently got confussed with the terms. Specifically, applying for a Customs overflight permit according to the 19 CFR 122.25 (c)(2) item speaks of listing a class of aircraft and another operators example suggests that it refers to a weight class (I, II, III, etc).

Terms as I understand right now: Class of aircraft in regards to FAR 1.1 and 61 for certification of airman means SEL, MEL, SES, helicopter, airship, etc and for certification of aircraft means airplane, rotorcraft, balloon, etc. Class in regards to a weight division, perhaps as used in ICAO terms - ???? Category in regards to 1.1 and 61 for certification of airman means airplane, rotorcraft, lighter-than-air, etc. and for certification of aircraft means normal, utility, transport, etc. Also for 1.1 it speaks of Category A and B talks to transport category rotorcraft and Part 97 refers to Cat A, B, C, D, & E for approach category of aircraft based on 1.3 Vso. Then in 1.1 and part 91 we come to Cat I, II, III, IIIa, IIIb, & IIIc for ILS minimums. Then its aircraft classes for the purposes of wake turbulance separation (Pilot/Controller Glossary) heavy, large, and small (ICAO uses light, medium, heavy ?). Then large aircraft for aircraft over 12,500 lbs for aircraft cerification and type rating requirements. I feel like Abbott and Costello with who's on first! Anyway, maybe this helps or maybe more confused. Anyone have any other references for Class or Category pertaining to aircraft? Especially in regards to a weight class and 122.25?