Air Data Computer
Air Data Computer (ADC)
🧭 1️⃣ What is the ADC?
The Air Data Computer (ADC) is like the “brain” of the pitot–static system. It takes information from the aircraft’s air pressure sensors and calculates important flight data for the cockpit and flight control systems.
⚙️ 2️⃣ What Inputs It Uses
The ADC receives three main inputs:
| Source | Measures | Type of Pressure |
|---|---|---|
| Pitot Tube | Air pressure from airflow | Total Pressure (Pt) |
| Static Port | Air pressure outside the aircraft | Static Pressure (Ps) |
| Temperature Probe | Outside air temperature | TAT (Total Air Temperature) |
🧮 3️⃣ What the ADC Calculates
Using those inputs, the ADC computes:
| Output | Meaning | Used For |
|---|---|---|
| IAS (Indicated Airspeed) | Based on difference between total and static pressure | Airspeed indicator |
| TAS (True Airspeed) | IAS corrected for altitude & temperature | Navigation / FMS |
| Mach Number | Ratio of TAS to speed of sound | High-speed aircraft |
| Altitude (Pressure Altitude) | From static pressure | Altimeter display |
| Vertical Speed (VSI) | Rate of change of static pressure | Climb / descent indication |
| OAT / SAT | Outside air temperature | Performance calculations |
✅ These values are sent digitally to:
- PFD (Primary Flight Display)
- FMS (Flight Management System)
- Autopilot / Flight Director
- Transponder (for Mode C / Mode S altitude reporting)
💡 4️⃣ How It Works — Simplified
Pitot Tube (Total P) →┐
│
Static Port (Static P) → ADC → Airspeed, Altitude, Mach, VSI
│
Temp Probe (TAT) →───┘
It’s essentially a pressure + temperature calculator that converts these physical values into digital air data for the avionics system.
✈️ 5️⃣ Advantages of a Modern ADC
- More accurate (no mechanical lag like old analog instruments)
- Provides digital outputs to many systems simultaneously
- Enables redundancy (usually 2 or 3 ADCs for safety)
- Automatically corrects for known errors (position, compressibility, etc.)
✈️ 6️⃣ In Simple Words
The Air Data Computer takes air pressure and temperature, does the math, and tells the airplane how high, how fast, and how quickly it’s climbing or descending.