Empirical Earth · Flight & Navigation

Planes never “dip the nose” — and why that’s expected

The claim

“Pilots follow barometric pressure and never dip the nose, so the Earth can’t be a ball.”

What is measured

Holding a barometric “level” means following a pressure shell wrapped around a sphere. Following that curve changes the pitch by only ~0.0022°/s, about 8° an hour, far below what a pilot could see or feel. No visible nose-dip is what the globe predicts. More on refraction and the curve.

What would show this is wrong

a long cruise at fixed pressure altitude that measurably climbs away from sea level, or an attitude indicator that must be pitched down to hold altitude by more than the ~8°/hour the curve implies.

Sources

  1. Flight levels & the standard altimeter setting. At and above the transition altitude (18,000 ft in the US) aircraft set 29.92 inHg / 1013.25 hPa so all share one pressure datum for vertical link
  2. Airliner cruise attitude and angle of attack. In level cruise a jet holds a small nose-up pitch (about 2.5° for an A320 at cruising altitude) because the wing must fly at a few degrees of an link
  3. Rule of three & top of descent. The aviation “rule of three” (3:1 rule of descent): allow 3 NM of travel for every 1,000 ft of descent, so a descent from flight level 350 needs roughly 35×3 link
  4. The ILS glide-slope experiment. A flat-earth test flew a plane at a fixed altitude and measured the distance at which it intercepted an airport’s ILS glide slope. The flat and globe predicti link
  5. Attitude indicators: analog, digital and inertial. A vacuum-driven artificial horizon uses a spinning gyro erected to local vertical by a pendulous mechanism; a glass primary flight display link
  6. Flight data recorder pitch resolution. The FAA airplane flight recorder specification (14 CFR part 121, appendix M, and part 135, appendix F) sets pitch-attitude recording resolution at abou link
  7. Transport rate in inertial navigation. An inertial reference unit must continuously correct its computed vertical for the rotation of the local level frame as the vehicle travels over a curv link
  8. ADS-B barometric altitude encoding and the Q bit. In the airborne position message the 12-bit altitude field contains a Q bit: when set, barometric altitude is encoded in 25-foot increments; link
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