14 CFR § 25.531 - Hull and main float takeoff condition.

---
identifier: "/us/cfr/t14/s25.531"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "14 CFR § 25.531 - Hull and main float takeoff condition."
title_number: 14
title_name: "Aeronautics and Space"
section_number: "25.531"
section_name: "Hull and main float takeoff condition."
chapter_name: "FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "AIRCRAFT"
part_number: "25"
part_name: "AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "49 U.S.C. 106(f), 106(g), 40113, 44701, 44702 and 44704; Pub. L. 115-254, 132 Stat 3281 (49 U.S.C. 44903 note)."
regulatory_source: "Docket No. 5066, 29 FR 18291, Dec. 24, 1964, unless otherwise noted."
cfr_part: "25"
---


# 25.531 Hull and main float takeoff condition.

For the wing and its attachment to the hull or main float—

(a) The aerodynamic wing lift is assumed to be zero; and

(b) A downward inertia load, corresponding to a load factor computed from the following formula, must be applied:

where—

*n* = inertia load factor;

*C*<sub>TO</sub> = empirical seaplane operations factor equal to 0.004;

*V*<sub>S</sub><sub>1</sub> = seaplane stalling speed (knots) at the design takeoff weight with the flaps extended in the appropriate takeoff position;

β = angle of dead rise at the main step (degrees); and

*W* = design water takeoff weight in pounds.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5673, Apr. 8, 1970]