B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
General Maintenance Action; General Flight Cancelled / Delayed
Environment - Non Weather Related
I arrived at aircraft; passengers were boarded and [I] briefed the lead flight attendant. [Another Flight Attendant] told me the inbound Captain wanted me to know the windscreen was scratched and should be written up. [Lead flight attendant] spoke up and said as they were boarding in ZZZ a mechanic came up and looked at the windscreen. He and the Captain decided it could be written up on the return flight. I assumed they meant the windscreen was dirty. I looked at the windscreen and saw the Captain's had marks covering the entire windscreen looking as if the wiper had operated without a rubber blade. The First Officer's windscreen was marked also but not to the same extent. I reached out to see if I could wipe away the marks. The marks did appear to be scratches. I wrote up the windscreen as scratched and the field of vision impaired. Local maintenance came up to look. The mechanic was a seasoned professional having worked many years in Mexico City. After inspecting the windscreen and finding what looked like sand in the wipers he concluded the windscreen had been damaged due to a volcanic ash encounter. I asked what about the engines? We went out and looked. Both inlets appeared scuffed along the edges and the bullet noses were stripped of paint in a spiraling spotted pattern. The mechanic stated the damage was consistent with an ash encounter. The condition of the engines in conjunction with the windscreen led me to write up the engines as showing evidence of an ash encounter. I then refused the aircraft to expedite the handling of the passengers. Flight was delayed until the next day when another aircraft could be brought to us. We returned without further incident.
B737-NG Captain reported discovering during preflight that the cockpit windows and the engines showed sign of damage from a volcanic ash encounter.