Using a simulator, researchers at the University of Illinois conducted a study with 20 pilots who had no instrument training to see the survivability of an encounter with IMC conditions. All of them lost control, and the only variable was how long it took. The range was as short as 20 seconds to as long as 480 seconds with the average being 178 seconds. This was done in a fixed-wing simulator and I do not know of a formal study like this done with helicopters. My guess is a helicopter pilot with little or no instrument training would lose control in a much shorter time. Continued VFR flight into IMC conditions has caused many helicopter accidents.
For example, according to the National Transportation Safety Board a Bell Jetranger and an R44 helicopter were in route to Astoria, Washington when they encountered an overcast layer. A passenger in the Jet Ranger reported that the pilots of both helicopters were in continuous contact during the flight and as the weather conditions deteriorated, the pilot in the accident helicopter asked the pilot in the Jet Ranger what they should do. The witness reported the pilot in the Jet Ranger stated, “I’m going to go through it, stay right behind me.” The pilot in the accident helicopter agreed. The witness reported that when the Jet Ranger entered the fog, the accident helicopter was behind and above us. Approximately 30 seconds later; the pilot of the Jet Ranger stated, “Go back up… it’s too low. It’s much lower than we thought. Go back up right now.”
The witness stated that as the Jet Ranger ascended, the pilot attempted to contact the accident helicopter, however the attempts were unsuccessful. The Jet Ranger departed the area and was eventually able to land in Astoria. A search for the other helicopter was initiated and two orange life vests and miscellaneous debris were located floating in the water. The bodies of both pilots and passenger were recovered in the general area later that day. Numerous smaller pieces of helicopter wreckage were recovered from the water; however the majority of the wreckage was not located.
The pilot of the R44 held a commercial pilot certificate with rotorcraft-helicopter and instrument ratings. The pilot also held a flight instructor certificate with helicopter and instrument helicopter privileges. As an instrument instructor I am sure the pilot had practiced instrument flying with a vision restriction device. However, there is a significant difference between practicing with a hood and losing all visual references while under stress.