Aircraft Categories

[Deftone45075]

Twins are a different story, and having to jump to the next category is common for the reasons you posted. My post was soley directed to light, single engine arplanes tha stall below 50 knots in the landing configuration. 1.3 X 50 is 65. If your approach speed is 65, I don't know why poeple are shooting an approach at 90, a than increasing it even more to circle. If your already 25 knots above where you should be, than you have enough of a "buffer" as it is, in fact too much, and there is no reason to increase it anymore.

I think a lot of this has to do with what is taught when getting your IR in a single. I was taught ( and I'm aware of several schools that teach ) to fly the approach flaps up, at 90 knots. Why? If 1.3Vso is the approach speed, where did 90 kts come from? Just to get dow faster? And I never liked the idea of a flaps up appoach. Granted it is a Cessna or a Warrior we're talking about, but what happened to a stabilized approach? Flaps up, at 90 knots to DA or MDA and than cutting the power an trying to configure for landing in the last minute or less doesn't seem like a bright idea.

In the case of a non precision approach, yes, leave out some flaps. But not flaps zero. And whn it is an ILS, configure for landing, and be at the appropriate approach speed by the marker. If the approach is to mins, and at DA you only have the approach lights and continue to 100 ft., than all you have is 100 ft. to go from 90 knots with no flaps to 65 with full flaps. Thus I disagree with the training being conducted, for the schools who teach this way.

 

[Deftone45075]

I also wanted to respond to FlyChicago's remarks on system malfunctions and other abnormal circumstances. For wind gusts, I'd add half the gust factor to Vref and to my approach speed, up to 10 knots. At 10 knots of an increase, you'd have a 20 knot gust, which is some good wind shear, and i'd be looking for another place to land if possible. For flap malfunctions you would want to add some speed as well. But these are abnormal circumstances. Under normal conditions, in a 172 or the like, there is no reason to shoot an approach 25 knots above the correct speed. If your at 1.3Vso and have to circle, you can increase your speed and you won't have to move to the next category.

 

[stillaboo]

From the Jeppessen Instrument/Commercial manual:

"As you know, approach categories are based on 1.3 times the stall speed in the landing configuration. When executing a circling approach, just as you do during a straight-in landing, you must use the appropriate category minimums for your aircraft. However, if you operate at a higher speed than is designated for your aircraft approach category, you should use the minimums of the next higher category."

Refer Figure 7-41.

"If you are circling in a Category B aircraft, but you are operating at a speed above the Category B speed limit, you should [my emphasis] use the MDA and visibility requirement appropriate to Category C."

See the word SHOULD? Your category is determined by FAR 97.3(b), and is "based on a speed of 1.3 Vso (at max certificated landing weight)". How fast you fly the approach is not a factor in determining your category and its assigned minimums - though it should be!

There are all kinds of things one SHOULD do according to Jeppesen (and the AIM). There are also things you MUST do according to the FARs (unless your op. specs are approved to superseed the FAR's, of course).

If you choose to race an SR-71 on a simultanious approach in your 172 and he goes missed based on his higher minimums and you bend metal b/c the minimums you were using were never designed to allow you to see the runway environment at that speed, you can at least die knowing you approached in the legally correct Cat. and its minimums. Of course you violated many other FARS in the process, but, at least you prove the point.
------

Food for thought: can a 172 ever get to a SR-71's Vso w/o diving (What's Vne of a 172 anyway?)? Inquiring minds want to know.

 

[Deftone45075]

Perhaps one of the pieces would accelerate to the SR-71's Vso due to gravity. I say pieces, because most likely that's what would be left after exceeding Vne by a 100 knots or more on your way to reach the Vso of the SR-71. So after massive sructural failure, and if perhaps the engine block eventualy seperated, it's heavy enough that while falling to the earth it could approach the stalling speed of the Blackbird.

 

[100LL... Again!]

The Jeppesen Instrument/Commercial Manual is NOT a regulatory document.

If circling, you are required to use the higher mins.

The use of the word 'should' is simply the writer's expression.

Second of all, these manuals sometime contain errors in facts.


Here's a techie question for you:

You are circling at 1.3 Vso. You are in a 30 degree bank (to make the example simple). Vso=100 knots.


#1 What is your margin above stall?

#2 What is your loss in vertical component of lift if you do not pitch up to hold altitude?

 

[IP076]

Could you provide the reference that says you are "Required" to use the higher minimums for a circling approach?

Also, you're looking for the margin above Vso. I don't know about all of you, but, on a circling approach, I'm not usually in the full landing configuration. (Usually only partial flaps) This only makes that margin smaller.

The other place a lot of people get mixed up with circling approachs is the Distance a pilot has to maintain from the runway complex throughout the manuever. Yes, you must stay within the prescribed radius, but you must also stay within the prescribed visibility requirements on the approach procedure. You have to keep the runway in sight, correct?

You can be 1.2 nm from the runway and not run into anything, but if the vis requirements are 1 sm (.87 nm) and the weather is at mins, you have to keep it in tight to keep sight of the runway.

 

[ksu_aviator]

AIM
5-4-7. Instrument Approach Procedures
a. Minimums are specified for various aircraft approach categories based upon a value 1.3 times the stalling speed of the aircraft in the landing configuration at maximum certified gross landing weight. In 14 CFR Section 97.3(b) categories are listed as follows: ...

...b. Aircraft approach categories are also discussed in the U.S. Terminal Procedures (commonly called approach plates), which states, among other things, that "An aircraft shall fit in only one category. If it is necessary to maneuver at speeds in excess of the upper limit of a speed range for a category, the minimums for the next higher category should be used." If it is necessary, while circling-to-land, to maneuver at speeds in excess of the upper limit of the speed range for each category, due to the possibility of extending the circling maneuver beyond the area for which obstruction clearance is provided, the circling minimum for the next higher approach category should be used. For example, an aircraft which falls in Category C, but is circling to land at a speed of 141 knots or higher should use the approach category "D" minimum when circling to land.

Simply put, 1.3 Vso determines your category unless you are using a higher airspeed and then that becomes your new category.

 

[IP076]

Again, that is correct. Its just that you are not "required" by law to do that. Now, does it make sense? Yes. Is it law? No.

Note that paragraph in the aim also says "should".

Legally, all you have to do is use the category that corresponds with 1.3 Vso.

Now, if you were circling at 130 in a 172 and used Cat A mins and ran into a mountain, I'm sure 91.13 would probably come up.

 

[Timebuilder]

Thanks for posting that AIM reference. When I made my post above, I was away from my reference CD.

 

[ksu_aviator]

here is the internet reference to the aim



IP, if you want to argue technicallities, there are no laws that require you to do anything in aviation. Only regulations.

You are right that any thing you are told to do in the AIM is covered under 91.13 in that going against the FAA's advice is considered Careless and Reckless opeartion.

Lets look at this.

Vref is controlling. If operating conditions require a higher Vref, your category does change (refer to (97.3). In absence of Vref, Vso x 1.3 is then controlling and the same applies.

If you fly at a higher airspeed then 135 and 121 ops spec always refer to the highest speed used. Now maybe part 91 you can get away with it, but I don't think I'd try it. I can't find the specific reg right now, but I'm sure it exists. Either way, 91.13 will always bite you if the FAA wants to get you.