Sad news of a tandem-rotor CH-47 crashing as it was taking off at night with 31 American and seven Afghan troops on board. The crash followed a firefight in the Tangi Valley, Wardak Province. Most likely it was an aircraft operated by the Special Operations Aviation Regiment; my earlier post on SOAR is here.
News accounts say that a hit by a single rocket propelled grenade was probably the cause. The Eastern bloc RPG-7 has been a cheap, rugged, effective launcher for unguided projectiles.
The most commonly pictured warhead is the PG-7VL conical model carrying a shaped charge, but warheads also come in thermobaric and fragmentation varieties.
It's possible that the launch of a single RPG fragmentation round -- what some call the Golden BB -- was the cause but I'd be surprised. Early in the Russian invasion of Afghanistan, Afghan fighters tried aiming single RPGs at Russian helicopters but it hardly ever knocked a transport or gunship down, even under prime shooting conditions in the daytime. Aiming the unguided RPG accurately at night at a blacked-out, moving helicopter would be extremely difficult. It's even less likely that a single hit would be fatal.
So my speculation is that either a guided MANPAD missile was involved, or else a multiple-RPG ambush. Multiple RPGs were involved in the "Black Hawk Down" incident in Mogadishu.
Some of the most effective anti-helicopter tactics developed by Northern Alliance fighters against Russian helicopters relied on an ambush by heavy machine guns or multiple RPG launchers. If RPGs were used these were at a half-mile distance, fired simultaneously to use the timed warhead as a flak round. An unclassified US training manual on the RPG-7 is here.