What is PERF INIT on Boeing 737? (Performance Initialization – Fmc Page)

The Performance Initialization (PERF INIT) page is an essential component of the Flight Management Computer (FMC) system on the Boeing 737-800 aircraft. The FMC is responsible for managing various aspects of the flight, including navigation, performance calculations, and fuel management. The PERF INIT page specifically deals with initializing and configuring the aircraft’s performance parameters before a flight.

By inputting accurate performance data into the FMC, pilots can ensure the aircraft operates within optimal performance limits during different stages of flight. This data includes factors such as takeoff weight, flap configuration, runway conditions, and cruise altitude. The FMC then uses this information to calculate essential performance values, such as takeoff speeds, climb rates, fuel consumption, and range calculations.

Using the Performance Initialization – FMC page

Before each flight, pilots must access the PERF INIT page on the FMC to input the necessary performance data. This page allows pilots to enter values or select pre-determined values for different parameters, ensuring accurate performance calculations for the specific flight.

One of the key inputs on the PERF INIT page is the aircraft’s gross weight, which includes the weight of the aircraft, fuel, payload, and passengers. This weight information is crucial for the FMC to determine the appropriate takeoff speeds, climb rates, and fuel requirements for the aircraft.

The pilots also enter the flap configuration on the PERF INIT page. The flap setting affects the aircraft’s lift characteristics during takeoff and landing. Different flap configurations have different performance implications, and the FMC takes this into account when calculating speeds and climb rates.

An essential piece of information entered on the PERF INIT page is the wind data, including the wind direction and speed at various altitudes along the planned route. The FMC utilizes this information to calculate more accurate fuel predictions, optimize the flight path, and adjust the thrust settings to compensate for wind conditions.

The Importance of Accurate Performance Initialization

Accurate performance initialization is vital for the safe and efficient operation of the Boeing 737-800 aircraft. By inputting precise data into the FMC, pilots can optimize the aircraft’s performance, minimize fuel consumption, and ensure compliance with regulatory requirements.

Using incorrect performance data can lead to suboptimal flight performance, increased fuel consumption, and potentially compromised safety. For example, entering a higher weight than the actual gross weight could result in incorrect takeoff speeds, longer takeoff rolls, and reduced climb performance. On the other hand, entering a lower weight may lead to excessive speeds during takeoff, compromising the aircraft’s ability to safely lift off the ground.

Additionally, accurate wind data is crucial for optimal flight planning and fuel efficiency. Incorrect wind inputs can result in inaccurate fuel predictions and inefficient flight paths, potentially causing the aircraft to carry more fuel than necessary or leading to unforeseen refueling requirements.


The Performance Initialization – FMC page plays a crucial role in the operation of the Boeing 737-800 aircraft. By accurately inputting performance data, pilots can ensure the aircraft operates within its optimal performance limits, maximize fuel efficiency, and comply with safety and regulatory requirements.

It is essential for pilots to thoroughly understand the purpose and functionality of the PERF INIT page to ensure accurate performance initialization. Proper utilization of this page enables pilots to make informed decisions about takeoff speeds, climb performance, and fuel management, ultimately leading to safer and more efficient flights.

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