Situations arise in which there is no time to pray a silent Amidah first and then recite an Amidah repetition. For example, sometimes a number of people must leave for work and without them there is no minyan. In such cases, the Amidah repetition is not recited. In order to ensure that their prayer will be in a minyan, everyone prays silently together. So as not to miss Kedushah, the chazan starts reciting the first three berachot aloud, the congregation responds to Kedushah, and the chazan and the congregation continue from Birkat Attah Chonen to pray the rest of the Amidah silently (Rama 124:2).
Likewise, in a small minyan, in which some of the members greatly prolong their prayer and the others find it difficult to wait until they have finished, since they are rushed to be on their way, they are permitted to forgo Chazarat HaShatz. Instead, the chazan recites the first three berachot aloud in order to recite Kedushah. Although we learned that in extenuating circumstances it is permissible to recite Chazarat HaShatz while a few of the nine are still standing in prayer, nevertheless, l’chatchilah it is preferable not to enter into this uncertainty and to forgo the recital of the Amidah repetition altogether.
When there is a minyan whose members normally chatter and there is concern that there may not be nine men responding Amen to the chazan, there is reason to consider canceling Chazarat HaShatz. Perhaps it would be best to forgo its recital in order to reduce the desecration of Hashem’s Name caused by the talking during the Amidah repetition. Still, the prevalent minhag is not to cancel the Amidah repetition in a place that people normally chatter during the prayer service. All these laws must be decided by the local rabbi.
When the chazan begins reciting the first three berachot out loud, there are two customs as to when the congregation starts to recite the silent Amidah. Some are accustomed to start after the chazan finishes Birkat HaKel HaKadosh (Mishnah Berurah 124:8), and others are accustomed to starting to pray along with the chazan (Kaf HaChaim 124:10). It seems that it is best to recommend starting to pray with the chazan in Shacharit so as not to pause in the middle of Birkat Emet V’Yatziv. In Minchah, it is best that whoever normally prolongs his prayer starts to pray with the chazan so that he can conclude his prayer and respond to the Kaddish after it. Concerning a person who is used to praying quickly, it is best that he starts praying after the chazan concludes “HaKel HaKadosh.”
When Chazarat HaShatz is not recited in Shacharit, and there are Kohanim present, in order not to lose out on Birkat Kohanim, it is best that the Kohanim wash their hands before praying and stand to recite the Amidah in the place in which they normally raise their hands to recite Birkat Kohanim. When the chazan reaches Birkat Retzeh, he begins to pray aloud again, so that the Kohanim can bless Israel after the conclusion of Birkat Modim. Whoever is reciting the same berachah in his silent Amidah should respond Amen to it (see Mishnah Berurah 128:71).
. The Radbaz (section elef 165) writes that the Rambam cancelled the silent prayer due to the people who chattered during the Amidah repetition. He instructed the chazan to recite the prayer aloud, and the well-versed to pray silently with him. However l’chatchilah, it is clearly proper to pray twice, as the Chachamim instituted. See Yalkut Yosef 124:17 and Yechaveh Da’at 3:16 who summarize the obligation to recite Chazarat HaShatz and conclude that if there is concern that there will not be nine people to respond Amen, it is preferable not to recite Chazarat HaShatz at all.