What is PMA on Boeing 737? (Permanent Magnet Alternator)

The Permanent Magnet Alternator (PMA) is an essential component of the Boeing 737 aircraft’s electrical power system. As the name suggests, it is an alternator that utilizes permanent magnets to generate electrical power. This article will delve into the details of the PMA on the Boeing 737, its function, and its significance in ensuring reliable power supply during flight.

How Does the Permanent Magnet Alternator Work?

The Permanent Magnet Alternator (PMA) on the Boeing 737 works on the principle of electromagnetic induction. It consists of a rotor, stator, and permanent magnets. The rotor, when rotated, induces an electric current in the stator windings through the interaction between the rotating magnetic field generated by the permanent magnets and the stationary windings in the stator.

As the engine operates, it drives the PMA rotor, which spins the permanent magnets. The rotation of the magnets generates an alternating magnetic field, which in turn induces an alternating electric current in the stator windings. This current is then rectified to direct current (DC) through a diode bridge, allowing it to be used to power various aircraft systems and charge the onboard batteries.

Significance of the Permanent Magnet Alternator

The Permanent Magnet Alternator plays a crucial role in the electrical power system of the Boeing 737. One of its main functions is to generate electrical power to meet the needs of the aircraft’s systems and equipment. These include powering the avionics, cockpit instruments, lighting, communication systems, hydraulic systems, and more. Without a reliable power source, the safe and efficient operation of the aircraft would be severely compromised.

The PMA also serves as a backup power source. In the event of an unexpected failure or a loss of power from the primary generator, the PMA can continue to supply essential electrical power to critical systems, allowing the flight crew to maintain control of the aircraft and safely land.

Furthermore, the Permanent Magnet Alternator contributes to the overall efficiency of the electrical power system. Its design and use of permanent magnets eliminate the need for a separate excitation system, reducing weight and complexity. This results in a more compact and lightweight alternator, improving fuel efficiency and reducing the aircraft’s overall weight.


The Permanent Magnet Alternator (PMA) is a vital component of the Boeing 737 aircraft’s electrical power system. It harnesses the principles of electromagnetic induction to generate electrical power necessary for the functioning of various aircraft systems. Its significance lies not only in the provision of power but also in its ability to serve as a backup power source, ensuring the safety of the aircraft and its occupants.

The PMA’s design and use of permanent magnets contribute to the overall efficiency of the electrical power system, enhancing fuel efficiency and reducing weight. As technology continues to advance, the Permanent Magnet Alternator will likely undergo further improvements and advancements to meet the evolving needs of the aviation industry.

For More: What is VBV on Boeing 737? (Variable Bypass Valve)