On October 13, 2012, about 0920 eastern daylight time, two helicopters in a flight of five, a Hughes 369A, N369SN (Chalk 3), and another Hughes 369A, N546 (Chalk 4), collided during hover-taxi while landing at Brandywine Airport (OQN), West Chester, Pennsylvania. The 3 occupants in Chalk 3 and the 2 occupants in Chalk 4 were not injured. Chalk 4 sustained substantial damage to all four main rotor blades and the tail pylon. Chalk 3 sustained substantial damage to the left landing skid. Both helicopters were operated under the provisions of 14 Code of Federal Regulations Part 91as personal flights. Visual meteorological conditions prevailed. The helicopters were part of a flight of 5 helicopters that attended an annual all-helicopter airshow.The pilots of Chalk 1, 3, and 4 provided written statements and their statements were consistent throughout. They each said that "Flight Lead" was in Chalk 5; the trail aircraft. According to their statements, the flight arrived in trail formation and overflew runway 09 at 1200 feet and 60 knots. Chalk 1 stated he entered left traffic, and while on the left base leg for landing, Chalk 3 announced airplane traffic on final approach to Runway 09. Chalk 1 stated he turned left prior to the runway, and initiated a go-around on the north side of the runway. Flight lead, in the trail aircraft, then announced over the flight's internal radio frequency to, "Break left or land." According to Chalk 3, he then "initiated a steep approach" to land on runway 09, and while he maintained visual separation from Chalk 2, noticed the rotor disk of another helicopter immediately below and to the right of his just as contact between the two was made, which separated the left landing gear skid. Chalk 3 then egressed his passengers from a hover, and repositioned the helicopter back to LNS in order to avail him of air traffic control and crash/fire/rescue services. The helicopter landed without further incident. According to Chalk 4, Chalk 1 announced a go-around, but Chalk 5 gave the command to break left or land. At that point, he had Chalks 1, 2, and 3 in sight. Chalk 4 then confirmed the airplane traffic was "no factor" and had initiated a go-around on the south side of the runway. When he looked back on the formation in front of him, he had only Chalk 2 in sight, and had lost visual contact with Chalks 1 and 3. Chalk 4 then performed a "normal" approach to a 5-foot hover over the runway centerline, began a hover-taxi to parking, and about 20 seconds later "felt" the contact with the other helicopter. He then landed the helicopter without further incident. The pilot of Chalk 4 held a private pilot certificate, with a rating for a rotorcraft-helicopter. He reported 586 total hours of flight experience, of which 253 hours were in the accident helicopter make and model. The pilot of Chalk 3 held a commercial pilot certificate, with a rating for a rotorcraft-helicopter. He reported 1,617 total hours of flight experience, 92 hours of which were in the accident helicopter make and model. Each of the accident helicopters had 100-hour inspections performed during the year prior to the accident, and each pilot reported there were no mechanical deficiencies with either helicopter that would have prevented normal operation. Examination of the Rotorfest 2012 Briefing slides revealed that the Chalk order briefed on the slides was not the Chalk order flown. There was no slide that provided guidance for loss of visual contact or inadvertent IMC procedures. There was no slide that identified "Flight Lead" would fly from the trail position of the formation. Examination of military and Formation and Safety Team (FAST) training documents revealed that flight lead was always the lead aircraft in a given multi-ship formation. While the air mission commander (AMC) may fly from any position in the formation, the lead aircraft always maintained the role of flight lead. Following in-flight formation changes, the aircraft assuming the lead position in the flight, assumed the role of flight lead. Army Field Manual (FM 3-04.203) Fundamentals of Flight, Chapter 6, Multi-Aircraft Operations stated: FLIGHT LEAD (TEAM LEAD) 6-8. Flight (team) lead and wingman are roles flight members fulfill based upon their positions within the flight. Team lead is used to denote the flight lead for two aircraft operating in teams. Flight lead is the formation leader designated by the AMC and is generally the most proficient PC (pilot in command). Flight leads are selected based on ability and demonstrated knowledge of missions and tactics, and local SOPs. The flight lead's responsibilities include navigation, en route communication (between flight members, ATC, and supported units), obstacle and threat avoidance, wingmen position awareness, and the energy states of all aircraft. The AMC may delegate some of these duties throughout the flight. Chalk 2 should always be prepared to lead the flight. FORMATION LANDING 6-41. All aircraft touch down at the same time while maintaining their relative positions within the flight. The rate of closure throughout approach and landing is somewhat slower at night than during the day. Flight lead should maintain straight-and-level flight until the desired approach angle is intercepted. Lead then maintains a constant approach angle and, where terrain and obstacles permit, makes the approach to the ground avoiding hovering turbulence and brownout or whiteout conditions. If the rate of closure is too fast, the aviator should avoid S-turns to lose airspeed. Instead, execute a go-around if unable to slow to the appropriate airspeed, especially with heavily loaded aircraft. 6-42. Lead must plan to touch down far enough forward in the PZ/LZ to provide sufficient landing space for the entire flight.