Above FL180

[nickname]

Had some flights recently between 160-180. ATC gave a block between 170-190 and I didn't go above 180 due to mask and operating limitations. But, it had me wondering, anyone that has PIREPs or data points on operating higher? On my DA40 the altitude pre-select didn't allow for above 165 but on the DA42 it allows above 180.

[ememic99]

Obviously performance reduces but not dramatically and I believe that -VI still operates fine, having in mind that DA62 (with practically same engines) is certified to FL200. I’ve flown DA42TDI (CD-155) few times above FL180 due to icing conditions below and while it’s not optimal, it’s still ok. I have data somewhere and I’ll share it once I find it.

[Boatguy]

The plane is fine. What about the pilot?

[ememic99]

The plane is fine. What about the pilot?

Measured saturation was fine and subjective feeling was ok still using cannula although I had mask prepared.

[ememic99]

Here are average data.

FL200:
- 75% 127 KIAS, 177 KTAS, 2300 RPM, 13.2 GPH
- 70% 125 KIAS, 174 KTAS, 2170 RPM, 12.2 GPH

FL190:
- 77% 130 KIAS, 176 KTAS, 2300 RPM, 13.8 GPH
- 75% 130 KIAS, 176 KTAS, 2270 RPM, 13.6 GPH
- 70% 126 KIAS, 172 KTAS, 2130 RPM, 12.2 GPH

[CFIDave]

When I visited the Austrian factory years ago to pick up my new DA42-VI and ferry it across the Atlantic, the Diamond pilot who accompanied me on the trip said that the factory had flown a DA42-VI above 30,000 feet. I'm certainly not recommending that, but it demonstrates that Austro engines should have no problem operating in the low 20s, if needed for example to top bad weather.

[meowmeow]

Interesting experiences and numbers to know!

(That said, aren't aircraft operating limitations mentioned in the AFM (mine: 2.11 The maximum operating alt is 18,000 ft) regulatory - so one may actually not go into class A with a Twin Star - or am I missing something..?

[ememic99]

Interesting experiences and numbers to know!

(That said, aren't aircraft operating limitations mentioned in the AFM (mine: 2.11 The maximum operating alt is 18,000 ft) regulatory - so one may actually not go into class A with a Twin Star - or am I missing something..?

If you have to go above weather and you know FL200 makes difference, you just ask and climb. ATC will always accommodate such request traffic allowing.

[CFIDave]

Interesting experiences and numbers to know!

(That said, aren't aircraft operating limitations mentioned in the AFM (mine: 2.11 The maximum operating alt is 18,000 ft) regulatory - so one may actually not go into class A with a Twin Star - or am I missing something..?

You are correct that the maximum operating altitude is regulatory, so legally it should not be exceeded. When certifying the DA42-VI, Diamond chose to limit the plane's operation to altitudes of 18,000 feet and below -- not necessarily because the plane couldn't be safely flown above 18K, but for liability, business, competitive or other reasons.

In reality nobody enforces this limit if you exceed it. I've had multiple occasions when flying our Epic E1000 (with a maximum certified operating alt of FL340) when ATC has asked if we could accept FL350 to help resolve potential traffic conflicts. We've always declined to fly that high, one reason being that at RVSM altitudes above 28,000 feet you legally MUST fly on autopilot due to the tremendous closing speeds (e.g., more than 700-800 knots) with other traffic passing only 1000 feet above or below you. I'm not sure our GFC700 autopilot will permit climbing above FL340. We'd also likely experience cabin pressures above 10,000 feet if we flew above FL340.

You have a different set of considerations with the DA42-VI. The similar DA62 (with which the DA42 used to share its type certificate) is certified to 20,000 feet, and you don't have to worry about cabin pressurization. But you are supposed to use a mask instead of a cannula when above 18,000 feet, which is far less comfortable and requires use of a different microphone. I know multiple Cirrus SR22T (certified to 25,000 feet) pilots who won't fly above 18,000 feet for this reason.

[ememic99]

Interesting experiences and numbers to know!

(That said, aren't aircraft operating limitations mentioned in the AFM (mine: 2.11 The maximum operating alt is 18,000 ft) regulatory - so one may actually not go into class A with a Twin Star - or am I missing something..?

But you are supposed to use a mask instead of a cannula when above 18,000 feet, which is far less comfortable and requires use of a different microphone. I know multiple Cirrus SR22T (certified to 25,000 feet) pilots who won't fly above 18,000 feet for this reason.

Being supposed and really needing a mask are two different things I tested this on several occasions with oxymeter and didn’t notice any difference between FL180 and FL200.