In Lord of the Flies, who was in charge of maintaining the signal fire the night of the aerial battle? Why did they not see the aerial battle?

At the beginning of Chapter 6, an aerial battle takes place ten miles above the island. During the aerial battle, a paratrooper is shot out of the sky and descends towards the island, eventually landing on the top of the mountain. Samneric were in charge of maintaining the signal fire and were supposed to take turns sleeping and keeping the fire lit. Since both of them have a tendency to follow one another, they both end up falling asleep and do not witness the aerial battle that takes place in the sky. They wake up to find that they've let the fire dwindle to a pile of ashes and frantically begin to blow on the small embers to relight it. After they get the fire going, Eric notices a shadow of something on top of the mountain. Samneric hold onto each other as they witness what they think is the "beast." Samneric mistake the dead paratrooper's hanging corpse for the "beast" and race down the mountain as fast as they can to tell the boys what they've just witnessed.