Cruising at 17,900ASL: Is it legal? No. Is it prudent? No.

[sdjfkosdjf]

baffling

[sanjet]

I dont think aircraft are allowed to cruise at FL180, am i wrong?

[bcflyer]

-Maintaining 17,500 will provide at least 500`separation with any traffic the controller might have at FL180. Flying at 17,900, on the other hand, provides almost no separation with traffic at FL180.

Could be absolutely no separation if you take into account traffic at 180 will have the altimeter set to standard while the 17900 guy is still at their last setting. Makes a HUGE difference some days!!

[Dave T]

This is not a good reason but I imagine sometimes it's just crews not paying attention. About to hit 180 and remembering they don't have a clearance yet or are anticipating one right away.
Not a valid excuse but I could see it happening.

[FamilyGuy]

What about 60100'? Is that prudent and legal?

[Dust Devil]

What about 60100'? Is that prudent and legal?

not much to bump into there

[FamilyGuy]

Habu's are retired save I think 1 at NASA. U2's still fly almost reguarily. However there is more capable of being up there than that - . Civil at FL590 is still a rare occasion but it does happen. I also think anything manned up there has slightly better equip than TCAS....

Same classification diff and same rules apply although I agree the big sky theory is bigger up high. Although - anywhere its busy there should be class B under 180 so ATC should in theory know about the traffic above 12500 - just as they "should" (don't always) know about any VFR above FL600. I guess that wasn't the original point though

[Pygmie]

...Although - anywhere its busy there should be class B under 180 so ATC should in theory know about the traffic above 12500...

I know of a couple examples where that is definately NOT the case.

[Lost in Saigon]

I remember reading about privately owned F-104's.........

It might be able FL605.....

The F-104G was significantly lighter than the other Century Series fighters and, with its small wing, had the highest wing loading of the group. Maximum speed is Mach 2.0 at 35 000 feet and Mach 1.13 at sea level. Initial rate of climb at sea level is a spectacular 48 000 feet per minute. In May 1958, a world speed record of 1404 miles per hour was set by an F-104, and a record zoom-climb to an altitude of 91243 feet was made.

[Lost in Saigon]

Here is a privately owned F-4 that could probably do FL600.

http://www.collingsfoundation.org/tx_f-4dphantom.htm

And this........

http://www.nasa.gov/centers/dryden/news ... -DFRC.html

[ywgatc]

Could be absolutely no separation if you take into account traffic at 180 will have the altimeter set to standard while the 17900 guy is still at their last setting. Makes a HUGE difference some days!!

You're actually wrong there. If FL180 is usable by atc, then the altimeter is 29.92 +. Therefore, when transitioning from the altimeter setting region to the standard altimeter region, you will show a lower altitude when you change to 29.92 (assuming the altimeter is above that, if it's exactly 29.92, then, obviously you would be showing the same alt.). So to cruise at FL180, you would have to climb higher, therefore creating extra spacing between you and the other a/c. Same thing in reverse. If you're flying at FL180 on an altimeter setting of 29.92, and the altimeter setting is 30.09 when you're cleared down, you're going to show FL182 after making the switch but before starting down. All that said, if an a/c popps up on RADAR at 17,900, I'm gonna be a little upset.....illegal, and not safe. Keep in mind that our tolerance is +/- 200 ft. So I'm okay with an a/c assigned FL180 flying at FL178. If the altimeter setting is 29.92, and you're flying VFR at 17,800' ASL hoping for FL190 on RADAR contact in the opposite direction, you tell me what's going to happen.