ForeFlight's "By Altitude" custom performance profile builder structures its data columns around pressure altitude rather than density altitude because that is the framework used in virtually every FAA-approved Pilot Operating Handbook and Approved Flight Manual. Aircraft performance certification under Parts 23 and 25 involves flight testing at known pressure altitudes and measured outside air temperatures. Manufacturers then publish performance tables organized by pressure altitude, with temperature as a separate input axis. ForeFlight replicates this structure so that pilots entering custom data can transpose figures directly from the POH without conversion. The application handles temperature correction internally, accepting OAT or ISA deviation as a separate variable alongside the pressure altitude entry, effectively computing density altitude effects within the calculation engine rather than requiring the user to pre-derive it.
The conceptual confusion between pressure altitude and density altitude is understandable, because density altitude is the operationally meaningful number — it represents the actual aerodynamic environment the aircraft experiences. However, density altitude is a derived value, calculated by correcting pressure altitude for non-standard temperature. It cannot be read directly from any cockpit instrument without additional computation. Pressure altitude, by contrast, is directly and immediately readable: set the altimeter to 29.92 inHg and read the indicated altitude. This measurability makes pressure altitude the practical organizing variable for performance charts. When a pilot enters pressure altitude and OAT into a ForeFlight custom profile — or into a conventional POH chart — the system resolves to the same performance output that a standalone density altitude calculation would produce, just through a different computational path.
For pilots building custom profiles for aircraft outside ForeFlight's default database — common among operators of older certified singles and twins, light sport aircraft, niche turboprops, or foreign type certificates — understanding this distinction is operationally critical. Entering data into the wrong altitude reference will produce systematic performance errors across the entire profile, potentially underestimating takeoff roll or climb performance at high-elevation or hot-day conditions. The correct workflow is to pull pressure altitude columns and corresponding OAT rows directly from the POH performance charts and enter them without pre-converting to density altitude. ForeFlight's temperature input field then reconstructs the density altitude relationship during flight planning calculations.
This question reflects a broader challenge in the transition from paper POH performance planning to EFB-based digital performance management. Many pilots have been taught to think operationally in terms of density altitude — a habit reinforced by preflight weather briefings, hot-and-high training scenarios, and mountain flying curricula — without fully internalizing that density altitude is a computed intermediate result rather than a published data standard. As EFBs including ForeFlight, Garmin Pilot, and others expand their custom performance profile capabilities to serve the long tail of aircraft types not natively supported, pilot understanding of how POH certification data is structured becomes increasingly relevant. Operators conducting Part 91, 91K, or 135 operations in aircraft with custom EFB profiles should verify that their data entry methodology matches the application's expected input format and cross-check outputs against POH figures at representative pressure altitude and temperature combinations before relying on the profile for operational planning.