The Importance of Monitoring Aircraft Vibrations

Aircraft vibration is not something to be written off. If parts aren’t balanced correctly, you can risk cracking, failed avionics, and loss of engine performance. This can also contribute to metal fatigue which, if left unrepaired, can lead to potentially catastrophic engine failure. This is why monitoring aircraft vibrations is one of the most important aspects of aircraft maintenance.

In aviation, vibrations are measured on a severity scale that ranges from 0 to 1.25 IPS (inches per second). For reference:

• 0 – .07 IPS is considered “good”
• .07 – .15 IPS is considered “fair”
• .15 – .25 IPS is considered “slightly rough”
• .25 – .5 IPS is considered “rough”
• .5 – 1.0 IPS is considered “very rough”
• 1.0 – 1.25 IPS is considered “dangerous”

Overall, when conducting a vibration analysis, the total vibration is the sum of contributions from moving components located within the engine, gearbox, and/or prop/fan. This can make utilizing a vibration analyzer and balancing equipment complicated, and that’s not considering the structural characteristics of aircraft that contribute to complications as well. For instance, where the vibration sensor is located and the type of mount used will affect how the vibrations are felt and distributed. When performing aircraft maintenance it’s important to always verify the OEM’s recommendation for sensor and mount installation. This also means utilizing the correct vibration monitoring equipment to ensure accurate measurements.

What Causes Engine Vibration

Vibrations are most often caused some type of imbalance. Rotating components that have uneven mass distribution can contribute significantly to vibration during flight. Proper vibration monitoring and balancing equipment is needed to measure and rectify this issue. A portable vibration analyzer with balancing capabilities can help measure, identify, and possibly correct the imbalance.

What Causes Imbalance?

An imbalance can be caused by a wide range of issues including replacement fan blades and damage from impacts during flight. Over time, wear and tear can also contribute to imbalances and so can corrosion of components. Care should be taken to monitor the aircraft for any signs of wear or damage to ensure safety during flight.

Monitoring Aircraft Vibrations

Typically, the manufacturer of the engine will specify when maintenance should be conducted. This recommended schedule should be strictly followed to ensure the continued operation of the engine and its components. Additionally, the FAA has issued directives that relate to engine safety. These directives can include recommendations related to testing and the safety limits of vibrations, as mentioned in the list above. While it’s important to heed these directives, you must also note that specific airlines and owners may require even stricter schedules, so communication is key depending on where you’re working.

As a general rule, engine testing should always be conducted following a recommended schedule, an in flight impact, or after a noted increase in vibration.

First and foremost you need to ensure you have the proper equipment in place to ensure maintenance and monitoring can be conducted correctly and safely. Without the right equipment, the engine could risk damage, and if an error occurs in flight the results could be catastrophic.