Side-by-Side Comparison
Avionics & Flight Operations
Altimeter Pressure Settings vs. Transponder Squawk Codes
Comparing 2 standards across 11 specifications. 11 key differences identified.
Comparing:
Altimeter Pressure Settings
Transponder Squawk Codes
Barometric altimeters compute aircraft height based on atmospheric pressure subscale settings: QNH (altimeter indicates true altitude above Mean Sea Level), QFE (altimeter indicates height above airport runway threshold), and QNE (standard 29.92 inHg / 1013.25 hPa for Flight Levels above transition altitude).
Air traffic control secondary surveillance radar (SSR) interrogates airborne transponders to receive 4-digit octal Squawk Codes (digits 0–7), with internationally reserved codes for emergency conditions: 7500 (Hijacking), 7600 (Radio Failure), and 7700 (General Emergency).
Specification Comparison Table
11 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standard Pressure Setting (QNE)
|
29.92 inHg (inches of mercury) = 1013.25 hPa (hectopascals/millibars) | — |
|
US Transition Altitude
|
18,000 ft MSL (Flight Level 180 / FL180) | — |
|
European Transition Altitude
|
Varies by airport (typically 3,000 ft to 6,000 ft AGL) | — |
|
Lapse Rate
|
1.00 inHg per 1,000 ft (~30 ft per 1 hPa/mb) | — |
|
Standard Authority
|
— | ICAO Annex 10 / FAA Order JO 7110.65 |
|
Digit Base
|
— | 4-digit Octal (0000 to 7777, providing 4,096 distinct discrete codes) |
|
Emergency Hijack Code
|
— | 7500 (Unlawful Interference) |
|
Emergency Comms Failure
|
— | 7600 (Lost Radio Communications) |
|
General Emergency Code
|
— | 7700 (Mayday / Immediate In-flight Emergency) |
|
VFR Standard (US/Canada)
|
— | 1200 |
|
VFR Standard (Europe/ICAO)
|
— | 7000 |