The Gemara relates the story of a bone that was broken through the skin and a chip became detached from it. So they brought it to Abaye, but he didn't know the answer. So it says that he waited for three Yom Tovim to try and find an answer. Hopefully that between those who gather then would be able to give an answer but no one was. On comes along Rav Ada bar Masno and suggest the owner to go to Rava. So he goes to Rava, and right away he says, "Don't you know the Mishnah?" And he gives him the answer. First of all, it would seem that Rava was not Oleh Regel or else he would have heard the question. And it seems like it was three yamim tovim in a row. Why was he not there? Secondly, in Rava's answer, he makes it seem like it's so obvious. Why did Abaye or anyone else not know what seems to be such a simple answer?
Heshi Kuhnreich
R' Heshi, it is wonderful to hear from you again!
1)
(a) A simple answer why Rava was not Oleh l'Regel is because he did not live in Eretz Yisrael. See Tosfos to Pesachim 3b, DH me'Alyah, who writes that Rebbi Yehudah ben Beseira did not go up to Regel since he lived in Chutz la'Aretz.
(b) However, in fact, it seems that the Gemara here is not really referring to anyone going to Eretz Yisrael. Abaye also lived in Bavel. If we notice, the Gemara here does not mention anything about "going up." Rashi writes that the Chachamim gathered together on the Regel. This seems to mean that they got together on Yom Tov but they all remained in Bavel.
(c) I want to suggest that Rava never left his city Pumbedisa, My source for this is the Gemara in Yoma, end of 53a, where we learn that Rava was a very close Talmid of Rav Yosef. Rabah and Rav Yosef said (Kesuvos 111a) that one is not allowed to leave Pumbedisa (because it was such a great Torah center) even to go to Bai Kuby.
2) The Rashba explains that since a piece had fallen off the broken bone, Abaye was in doubt that this may mean that the bone will not heal, so the animal is forbidden even though skin and flesh cover the majority of the bone.
Rava solved this doubt and said that since the Beraisa (the Tanu Rabanan on 76b) states, "if the bone broke and it sticks out," this suggests that it is Tereifah only if all of the bone, or the majority of the bone, stuck out and skin and flesh does not cover the majority of the bone, but if skin and flesh cover most of the bone it is Kosher. This proves that the animal will not die as a result of a minority of the bone sticking out. If so, it does not make a difference whether a minority of the bone stuck out, or actually fell off; in both cases it is Kosher.
Abaye was not so quick to permit the animal because he was concerned that the scenario he had been asked about may not be the same as the Beraisa. In his scenario, part of the bone had fallen off. Possibly this is worse than the scenario of the Beraisa where the bone merely stuck out and therefore might have a better prospect of recovery.
Rava possessed the "shoulders" to say that there is no difference between a minority of the bone breaking and a minority of the bone falling off.
May we be Zocheh to the Binyan Beis ha'Mikdash speedily!
Dovid Bloom