Question: What should someone do if he forgot to say Ya’aleh V’yavo in Shmoneh Esreh?
Answer: The Shulchan Aruch (Orach Chayim 124:10) rules that he should pay attention to the shliach tzibbur’s recitation, thus including himself in his prayer.
The problem with doing this is that a person who knows how to pray (a baki) generally may not use the services of a shliach tzibbur to fulfill his personal obligation to daven (Magen Avraham, Orach Chayim 124:1). The Mishnah Berurah, however, contends that this case is an exception since the person already davened (but forgot Ya’aleh V’yavo). In other words, he is relying on the chazzan only post facto.
Generally speaking, when a person wishes to be included in the prayers of a shliach tzibbur, he must listen attentively to every berachah the chazzan says. Since most people cannot do this, the Mishnah Berurah (Orach Chayim 124:40) rules that it is better for someone who forgot Ya’aleh V’yavo to say Shmoneh Esreh again rather than attempt to listen to every berachah of chazarat hashatz.
The Bei’ur Halacha cites Rav Akiva Eiger who adds a twist to this discussion. He notes that repeating the entire Shmoneh Esreh is not always necessary when someone forgets to say something. For example, if a person neglects to properly recite a portion of the concluding three blessings of the Amida, he only needs to return to the section which commences with R’tzeh. Thus, Rav Akiva Eiger rules that someone who forgot to say Ya’aleh V’yavo should not conclude Shmoneh Esreh and daven again, but rather should wait for the shliach tzibbur to begin his repetition of the Amida and start having kavanah from R’tzeh onward. Having kavanah for such a short period of time is not that difficult.
Another basis for not making a person daven again is as follows: Chazarat hashatz covers people who are not proficient in davening. Some poskim maintain that since a shliach tzibbur presumably has so much kavanah (the assumption being that he is quite pious), the congregants are “not proficient in davening” or even “ignorant” compared to him (see Ba’er Moshe, Orach Chayim 124:17 cited in the name of the Ayshel Avraham). Thus, a person who forgot Ya’aleh V’yavo may be included in the shliach tzibbur’s prayers even without listening attentively to every berachah.