Having been involved in aerial firefighting with rotary wing aircraft, I will add a couple of comments from my experiences.
All belly tanks, attached to Helicopters have emergency jettison of the water, I am not involved in fixed wing, but would assume they work on the same principle.
Tank doors are hydraulically operated, powered by the aircraft electrics. The default position for tank doors is always open, until the tank system master switch is activated.
Opening tank doors for the purpose of dropping water onto a fire is conducted by the Pilot operating a toggle switch attached to the cyclic. This switch is operated with one finger only, whilst controlling the aircraft. it is a two way switch, so on Helicopters is used to operating the pump to draw water into the tank.
If there is an issue with the tank opening whilst performing a drop, switching off the Tank master switch will then open the tank doors (Emergency Jettison).
Tanks as fitted to helicopters are not able to be jettisoned, only the water in the tank is.
Underslung bambi buckets are attached to the aircraft via the belly hook and can be dropped from the aircraft cargo hook via electrical or mechanical jettison.
Air Tankers would have a similar emergency dump system available. I can not see them being certified to drop with out Jettison ability.
Retardant as a rule is not dropped on active fire, but is dropped ahead of the running fire, in an area where asset protection is needed. This gives the widest swathe of retardant over an unburnt area, as well as a period of time for the product to get through the foliage. It is very effective for stopping of running fires, as long as they are not spotting ahead and able to jump the retardant line.
Fire Fighting aircraft operate under VFR, so I don't believe that they would have been transitioning to IFR after the drop, they may go to instruments to check wings level and positive rate of climb, particularly if about to enter smoke. Although the idea is to remain clear of smoke where ever possible when operating low level.
My opinion only, controlled flight into rising terrain (CFIT) due poor visibility.
Greg
