smartt1982
Topic Author
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Joined: Sat Nov 24, 2007 11:17 pm

737-800 Aproach Category C?

Sun May 16, 2010 10:23 pm

Regarding the 737-800, I have been told the 737-800 is in the C group of the approach categories. I have looked and this cetegory goes up to 141 Knots treshold crossing speed/1.3 x Vso, the 800 does depending on the weight does have a higher speed than this sometimes, I have been told that in the USA it could be sometimes put into the D category depeding on landing weight.

Why is it that the 800 is always a Cat C here in UK but can be a CAT D in the states

Many Thanks
steve
 
dispatchguy
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RE: 737-800 Aproach Category C?

Mon May 17, 2010 10:22 am

For straight-in approaches, the B738 is a Cat C // For circling approaches with the higher airspeeds, the B738 is a Cat D.
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smartt1982
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RE: 737-800 Aproach Category C?

Tue May 18, 2010 3:00 am

How come this is the case, ie that it cannot be in Class D for a straight In etc. I have heard that the authority can pick and choose what part of the category they want to follow, any truth to this?

Many Thanks
Steve
 
futureualpilot
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RE: 737-800 Aproach Category C?

Tue May 18, 2010 3:24 am

Most aircraft, particularly transport category aircraft circle at a higher speed than they approach at. Maneuvering during the circle requires a higher speed to stay safe. When you get lined up you can slow it down to ref.

Your category is based on your speed. If your weight requires a speed higher than 141kias you fly the category you fall under.
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smartt1982
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RE: 737-800 Aproach Category C?

Tue May 18, 2010 3:52 pm

Does that mean the 737-800 could be a CAT D for a straight in if due to its weight put the Vref over 141?
 
futureualpilot
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RE: 737-800 Aproach Category C?

Tue May 18, 2010 5:21 pm

Yes, when you fly an approach, be it straight in or a circle, the category you fall under is based on the speed you will be flying that approach.

It is possible that an airplane could fly an approach into one airport and need to be Cat D due to its speed but on the way back to the original airport be Cat C because its speed is different for one reason or another. Some companies might have restrictions on the category you fall under for a circle. I know for us, we're Cat C even if our speed is slower than the Cat C speed range.
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ThrottleHold
Posts: 547
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RE: 737-800 Aproach Category C?

Wed May 19, 2010 9:20 am

FAA TERPS protected area for a circling approach is much smaller than the protected area in most other parts of the world. 1.7 nm versus 4.2 nm.
 
smartt1982
Topic Author
Posts: 226
Joined: Sat Nov 24, 2007 11:17 pm

RE: 737-800 Aproach Category C?

Wed May 19, 2010 4:34 pm

Thanks for that guys, that all makes sense to me but I have been told that our 737-800 are always CAT C even though the apprach speed can be higher due to the regulators who can pick what part of the category they want to use to place it in that particulary category, so even though the speed could be higher it doesn't matter as they have used a different part of it, is this possible at all?

Thanks again
steve
 
bri2k1
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RE: 737-800 Aproach Category C?

Thu May 20, 2010 8:09 pm

Quoting smartt1982 (Reply 7):
the regulators who can pick what part of the category they want to use to place it in that particulary category
Quoting smartt1982 (Reply 7):
the speed could be higher it doesn't matter as they have used a different part of it

  Sorry I can't make heads or tails of that.

Why does category matter? Because the minimums can be different for the same approach with different aircraft categories. This makes sense: a faster plane has less time to react to indications of course deviation, so you would want to see terrain or obstacles with enough time to avoid them. A plane flying at 90 knots (Category B) with 1 mile visibility has about 40 seconds to react after seeing an obstacle straight ahead; a plane flying at 140 knots (top of Category C) has only 25 seconds to react in the same distance.

Circling and other non-precision approaches usually have higher minimums for faster airplanes. This makes sense too; by flying faster, the turn could deviate more quickly from the desired path, and again there's less time to react. A lot of straight-in precision approaches (ILS) will have the same minimums for each category.

By following the minimums applicable to a higher category, you might increase safety by having a greater margin for error. Following a lower set of minimums than the category applying to your selected approach speed, then, decreases safety. Why would anyone do this? (To be able to fly an approach otherwise not available due to minimums, perhaps. But that's quite a risk to take.) I'm pretty sure it's illegal, and even if it wasn't, you wouldn't catch me trying it.
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XFSUgimpLB41X
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RE: 737-800 Aproach Category C?

Fri May 21, 2010 3:54 am

The 800 is Cat D, 700 is Cat C....
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