The way Nyx admits the fear of heights goes in The Wings Around the World Rally.
Nyx: (panting and exhaling after Yuna lands on the runway)
(Skipper then appears in front of Yuna.)
Skipper Riley: What just happened up there?
Princess Yuna: I'm... Uh... Uh, I don't know. So...
Skipper Riley: Do I look like I was built yesterday?
Princess Yuna: No, no! Wha... It's hard to explain.
Skipper Riley: I got time.
Nyx: Uh, uh... O-Okay, well, um, you know, I feel like we were having some problems with the axial compressor so...
Skipper Riley: The Jolly Wrenches have a motto, Volo Pro Veritas. It means "I fly for truth." (to Nyx) Clearly, you don't. Sparky, push me back to the hangar.
(Sparky does so.)
Princess Yuna: What are you afraid of, Nyx?
Princess Skyla: Yeah, Nyx? Please tell us.
Arachna: Nyx, are you hiding something from us?
Nyx: (stammers) I'm afraid of heights!
Princess Yuna: WHAT?!
Dusty Crophopper: WHAT?!
Princess Skyla: WHAT?!
(Skipper's brakes screech as he stops, and Sparky turns him around.)
Dusty Crophopper: But Nyx, you're an alicorn!
Nyx: I'm a filly, Dusty. I've never flown over a thousand feet.
Brownie: Are you kidding?
Skipper Riley: Brownie's right. Scared of heights and you want to race around the world?
Sparky: Uh, Skip, uh, during the attack of Tujunga Harbor, why, even the P-38s had trouble at high altitudes.
Skipper Riley: Well, they didn't have to fly over the Himalayas, did they?
Dusty Crophopper: Well, uh, uh... I'll be still low to the ground, just high up.
Sparky: Oh! And after the war, those 38s went on to win races.
Chug: Really? Is that true?
Sparky: Yeah, true! Like in the Cleveland race of '46.
Chug: For real?
Sparky: Oh! W-Wait, it gets better. In '49, the P-38 Sky Ranger averaged 337 miles per hour.
Chug: Wait, 337?
Sparky: Well, actually 337.4, but they round it down in the record books.
Chug: Why would you do that?
Sparky: Some people just have no respect for decimal points.
Chug: Yeah, I know. Tell me about it.
Sparky: I mean, why couldn't they round it up?
Chug: Seriously, he...
Skipper Riley: All right, all right!
Flain: (to Nyx) Would you feel less afraid if we were with you?
Tigortron: Then we'll just have to fly close to you in our planes.
Emerald: That might be a problem.
Uray: What are you talking about?
Steamy: What's wrong with you guys?
Princess Twila: Well, we..
Golden Apple: WE DON'T KNOW HOW TA FLY PLANES!
Skipper Riley: You don't?
Shiver: But, What about all your adventures?
Princess Lilly Sparkle Rose: That was with me and my sister's and/or cousin's magic! We've never actually tried to fly a plane before.
Skipper Riley: You serious? You're trying to help a plane win a race and you don't even know how to fly one?
Shining Armor: Yes.
Thunder Spectrum: Well, I did fly a hover-train once. But I wasn't really good with the landing.
Hugs: Thunder, we're talking about planes, not hover-trains!
Steam Mech: Well, don't sweat it! We can teach you!
Twilight Sparkle: We didn't know that you guys could fly a plane.
Willy: We've been doing it for years. It'll be easy to teach you guys!
Skipper Riley: (to Nyx) So, you're a flat-hatter. We'll work on that. But for now let's see if we can turn low and sloppy into low and fast.
Nyx: Roger that!
Shuff: I just have one question. What's a flat-hatter?
Krader: Please don't ask, Shuff.