Date: 201508
Local time of day: 1201-1800
Location: BOI.Airport, ID
Flight conditions: Mixed
Weather elements / visibility: 0.5
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
ATC / advisory: Ramp BOI
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Other / Unknown
Anomaly: Aircraft Equipment Problem Less Severe; Ground Event / Encounter FOD
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: Aircraft Aircraft Damaged; General Maintenance Action; General Release Refused / Aircraft Not Accepted; General Flight Cancelled / Delayed
Contributing factors: Airport; Weather
Primary problem: Airport

Narrative: Aircraft arrived and a normal exterior inspection was conducted with no abnormalities noted.  There was a significant increase in wind strength from the south and roughly directly behind the aircraft causing a significant 'dust' storm and visibility reduction.  Shortly after a Ramp Agent informed us of a quantity of debris in both intake and exhaust sections of both engines.  The debris consisted of dust; sand; and small particles of stone ranging in size from one mm to about four mm in diameter and total quantity estimated to be between one fourth and one half cup in each engines hot exhaust section and about the same amount of debris in the intake section of the motor.  Additional greatly reduced amount of debris was also noted in the rear center cone vent section of each motor.   Upon notification of the FOD in each motor; Dispatch and Maintenance Control were consulted and contract maintainers were summoned.  Debris was vacuumed out of all sections of the motors and inspected with no other visible defects noted.  The engines were then motored at idle power for five minutes with no abnormalities noted from the flightdeck engine instruments.  Visual inspection of the motors unfortunately indicated additional debris being expelled from the hot section of the motor by the accumulation of new debris in the hot exhaust section and particles actively being expelled during engine spool down.  The local mechanics and Maintenance Control determined the aircraft required a more in depth inspection and grounded the aircraft pending a borescope inspection.  It is undetermined the level of damage or total cost of this disruption at this point; however; there is certainly a significant cost to this incident.The Boise Ramp Agents indicated the airport authority recently replaced all of the infield grass and areas between the runways and taxiways with a sand/gravel mix.  This concoction is now spread over all the ramp area; around the terminal; and on the taxiways and probably the runways.  I am certain this is the material that found its way into the motors.  I am astonished more aircraft have not fallen victim to this hazard.  In addition to the FOD hazard this gravel concoction is greatly reduces airport visibility during windy and gusty conditions such as the ones present on (date) where the wind and dust combination reduced visibility to less than one half mile.  It is my opinion this material is a significant hazard to aviation by the possibility of a simultaneous dual engine failure in or around the airport due to FOD ingestion of this gravel substance.  I recommend it be removed or mitigated ASAP.




Synopsis: Air carrier pilot reported FOD at BOI airport. Infield grass and areas between the runways and taxiways has been replaced with sand/gravel mix which blew into the jet engines.