How does the Harrier avoid engine damage when operating from dirt fields? The Harrier V/STOVL jet was designed in order for its users to be able to retain a functional air force even with all conventional airports destroyed; to this end, it can take off from, and land in, essentially any space large enough for it to fit into, potentially including unpaved dirt pads.

Unlike most jets designed to be capable of rough-field operations, the Harrier has no mechanism for preventing engine dirt ingestion, and, indeed, ingests considerable quantities of dirt and dust when operating from dirt fields:



(Image by @KeithS here at AvSE.)

How does the Harrier avoid engine damage from dirt ingestion during rough-field operations?
How does the Harrier avoid engine damage from dirt ingestion during rough-field operations?


The short answer is that they don't. They avoid using these FOD-laden strips if possible, but doesn't have any kind of active method for reducing FOD damage from debris ingestion.

This is supported by an RFP that NAVAIR put out asking for proposals to reduce FOD for the AV-8B:


  The AV-8B currently has the highest FOD damage rate in the U.S. DoD inventory which incurs a cost of more than $100M per year in engine removal, rebuild, and reinstallation, as well as decreased readiness and safety.


The method here is to just deal with it when it happens. The engine is removed, repaired, and replaced when a FOD incident occurs. 

The document also says:


  To date, NAVAIR has experienced more than eight Class 'A' mishaps in the AV-8B due to FOD


Where mishaps are defined: