Flew my MX7-180A from Oklahoma to Montana on Saturday. Got into Billings at 3:30pm and had a few interesting experiences:

Left Oklahoma City at 6:30am and first stop was Scott City, KS (TQK) at about 9am. Ground speed on the downwind was 168mph when I glanced at foreflight, while I was indicating about 110mph. At ground level it was a manageable 30kts mostly down the runway. However, taxiing to the fuel island was extremely difficult...had to basically ride one brake to handle the weathervaning.

Departed TQK at 9:30 for Buffalo, WY (BYG). At 10am, foreflight said my arrival time with my current ground speed was in 3.5 hours. An hour later at 11am, foreflight was saying I still had 4 more hours to go. The gusty tailwind had turned into a steady headwind. About 25kts there in Buffalo.

Got some more gas in BYG, and just before I departed for Billings, I had a flying friend that drove that route about an hour ahead of me tell me that the MT/WY state line was 2 mile visibility, snow, and ice, with cars in the ditch. Told me that I could climb above it and could get back down through broken layers as I got closer to Billings. Initially climbed to 9000...then 10,500...then 11,500...then 12,500. That still wasn't enough and after about 5 minutes I had to climb up to 13,600 to stay above everything. It was about 0 degrees F and the heater tried it's best, but couldn't quite keep up. About 20 miles from Billings I started to see large enough gaps in the clouds to circle down through. From 13,000 down to 6,000 was ice crystals and haze...made the carb pick up some ice in a hurry, but cleared it quick with the carb heat. Another sporty landing in Billings with a 25kt wind that was 40 degrees off runway heading.

Anyone here had their Maules up that high (13,600) or even higher?

I have had my M6 up to 14,500. A friend and I kept fighting strong but smooth mountain wave. So we just followed the next updraft and figured we would just ride it back down, but the down never came. At 14,500' we decided we better quit. The scary part was flying over a class B airspace and hoping the big airliners saw our little airplanes. Yes, we had oxygen.

I am aware of an M7 well exceeding 20k feet due to ridge lift. This was a forced climb as I am told and the pilot was not able to bring the plane down until he got past the ridge lift.

I have my M-6-235 up over 13,000 feet several times a week this time of year as part of my flightseeing business in the Colorado Rockies. I’ve occasionally had it up close to 18,000 sometimes with mountain wave assist, sometimes without any wind assist at all. These planes are great climbers.

14,500 on a hot summer day with the help of lift off the eastenr Sierra Nevada mountains.

180 HP

Had my M4-220 to 14.5 once trying to get above some turbulence on the last leg of the ferry flight home. Still bumpy up there, so I ended up down on the deck where it was a little bit smoother.

15,500' in NM in July looking for smoother air. 180hp.

14.5 in M5 trying to find smooth air

If you are in mountain wave there should be almost no limit as to a Maule's achievable altitude though hopefully you will be going in and out of the lift and sink bands. However, if you are going parallel to the lift you will continue to go up and up. Mountain wave is fun in a glider when you are prepared for that. New Zealand is famous for using mountain wave to do long cross countries and I have flown at 25,000 feet for 350 kilometers at 120K (no engine of course) that way. Also, mountain wave can go quite high as a new record for gliders was done in the Andes recently. They reached over 74,000 feet of course in pressure suits and special oxygen. Years ago a glider pilot set a record of 49,000 feet over the Sierras so don't think you will be safe if you avoid the Andes.

I forget to say that when one is in mountain wave the wind can be 80-100 knots but it will be perfectly smooth (so long as you are not below in the rotor.)

Testing a new to me, used O2 system one sunny day, got to 16,100+ over Williams Fork Mts, on the lee side of Gore Range. Still climbing at 100 FPM, M4-210

Just since this question came up, And it was such a nice day, and I as flying anyway, I went ahead and popped up to 17,900. On O2, of course. No wind today, so no mountain wave. Two on board, fifty pounds of gear give or taken and 30 gallons of fuel. Felt effortless.