To interrupt Tefila by writing

Question

For Birkat Hatora, writing is as speaking (SA OC 47,3): it is not allowed to write Divre Tora before Birkat Hatora.

1. If someone ask you a question when you are davening, can you write an answer or is it a prohibited interruption as speaking?
2. If someone want your signing for some reason, can you sign of is it an interruption as speaking, or is it a simple automatic movement of the hand?

Writing is not the same "instrument" than speaking which is used in Tefila, so the interruption is less perceptible. If we were praying by writing, to write something else would be surely an interruption.

May be that speaking and writing are equivalent from one point of view: they are not Devarim Shebalev, they are externalization of the thinking which originate from heart (Devarim Shebalev).

One a other hand, as it is possible to think somewhat else when in middle of prayer, it is possible to read an book in middle of prayer, and to enlight a statement on the book. It is also possible to write "Yes, No, Perhaps". So writing does not interrupt the flux of the speak.

One other side of the question is, following Rabenu Tam (Tosfot, Brachot 21b) who stated that without action of speaking, if you are hearing Kadish and Kedusha in middle of your prayer, it is an interruption because Shomea Keone. When you are writing, despite that you are not affiliated to an objective speaking, you are are affiliated to a speaking equivalent, and the lack of technical obstruction of the tfila speaking doesn't lead to a leniency.

I search an answer with a bit of moisture of lomdut.

Answer 1

The source of the psak concerning the need of Birkat Hatora for writing cited by Bet Yosef OC 47, is the Abudarham.

Here is a link obtained thanks to @Efraim, which links to Shut, particularly to Shut of Rav Chayim Zonenfeld, which we can help a lot to understand of the suggia.

1. First I looked in Eshel Avraham Botshatsh 47, 3. He stated that if someone writes the name of G-d or writes a Bracha, it is not "Bracha Levatala" or wast pronunciation of name of G-d. The only matter for which writing is equivalent to speaking is Mitsvat Tora learning. The source of this equivalence is that we have a commandment to write Tora and that the Tora was given in written form.

Despite that concerning Birkat Hatora, the Ktivat STaM style of writing is not needed, the learning by writing is equivalent in each writing style. For praying and blessing, writing is not regular and is nothing. So, we can infer from this that writing in a middle of a Bracha is not as speaking concerning interruption and is not an interruption at all.

2. But Shut Chavot Yair 194 said that writing is equivalent to speaking for everything except for testimony because of the verse "מפיהם ולא מפי כתבם". So It seems clear for him that writing is an interruption. [a little kushia, if at all: עדים החתומים על השטר כמי שנחקרה עדותן -- Testimonies signed on the written contrat are as if they testimonied and the testimony has be tested and aproved]

3. The Shut Simlat Chayim 46 concluded also that writing is an interruption (I am not entirely convinced).

Answer 2

Permitted only in a case of need (e.g., someone is about to do an aveira and you want to write them a note saying not to do it). Otherwise not allowed.