A water cannon salute, for those of us who don’t know what it means, is nothing but expelling plumes of water from the Aircraft Rescue and Firefighting (ARFF) trucks to form a series of arches under which the aircraft slowly passes.
It’s a beautiful sight to see & symbolically, the procession looks similar to a bridal party walking under a wedding arch. Usually 3,000 gallons (or 11,300 liters) of water is used by a single ARFF vehicle (or firetruck) for a single water cannon salute in about 2 minutes.
It is usually given as a mark of respect to either the pilot flying the aircraft or the aircraft itself. Categorically these can be:
- Induction of new aircraft in the fleet.
Pic: Water salute after ETIHAD inducting a new Boeing 787–900 aircraft in their fleet, welcoming the crew & passengers to the airport.
- Special occasions like Longest commercial flight:
Pic: Qatar Airways welcoming their Boeing 777 after its longest commercial flight between Doha & Auckland, New Zealand.
- Shutting down of operations
Pic: Last flight of Air Berlin after which they shut down their operations permanently in 2017.
- Farewell of a retiring captain on his last flight.
- As pointed out by Akshay Chandrasekar, water salute is also given when the aircraft is carrying a fallen service member.
- Water cannon salutes are also used to test the fire fighting equipment to ensure everything is working properly, as the use of water cannon is rare.
- In military environment, after an aircraft flies or hovers over saltwater, water cannon salute is given primarily to wash the aircraft to prevent corrosion.