Honestly, I was in a dilemma on locating "da" on that particular sentence when I corrected that statement recently however when I checked smilar usage in a "trusted newspaper" I saw it "one word [attached onto verb -Ipta] " and gone for it. But when Abla brought this issue up to discussion I had a chance to review it and Gokuyum´s digging into it helped me to rethink about it. And now I am inclining into "seperate dA ".

* Another thing ; Although sometimes conjunction "de" is pronounced as "te" [verbally]  whereas in written language it has to be seperated.

* But Locative "de" can not be seperated in both written and verbal language.

* The best way to check " dA " whether it should be written seperately or one word is ;

If the meaning of the word is almost the same when you remove "dA" from the word , then it is conjunction.

Zamanı olupta bana yardım edebilecekler lütfen bana yazsın.

Zamanı olup bana yardım edebilecekler lütfen bana yazsın.

I dont see much difference between two statements.

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* Under the light of all these,  the function of "da" in our sentence the clitic "de" follows "Ip" and it denotes and emphasize the relation between the actions.

1.Condition --> One must have time

2.Condition --> One must be capable [able to] help me.

3. wish [demand] --> I wish someone write to me

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If we put them all together ;

I wish someone, who is [at the position of ] able to help me providing that having enough time [to help me] , write [contact] to me please.

So my final conclusion on function of "da" in this context is "providing that"

We all make mistakes. It is very normal. I wrote adjective for "olup" but then understood that it was impossible for "olup" to be an adjective in any position in the sentence. Then I corrected it. I learnt many things from my mistakes. And I hope I will go on making mistakes again and again and someone will correct them and show me what I do wrong. Peace.

when I look at it from different angle I see "da" as  "and also ",

I wish someone, who is [at the position of ] able to help me and also having enough time [to help me] , write [contact] to me please.

I know, I messed the sentence up in English point of view  may be a native English speaker can tidy it up.

tunci´s sentence was not the first place where I saw this structure. I remember I have been wondering before what it is and how come it is not introduced in grammars. But this time my copy-paste finger worked very fast and I caught it before the ink dried. Good.

Thank you, gokuyum and tunci. It´s a joy to see how you two cooperate.

You are a wise man Gökuyum.

You too my friend.

Perfect harmony.

Without "da", YOLLARIMA BAKIP HEP BOYNUNU BÜKMÜŞSÜN, the implication is that the speaker has first hand knowledge of the other party waitıng for his return (That he has physically and personally observed the other party waiting for his return).

With "da", YOLLARIMA BAKIPDA HEP BOYNUNU BÜKMÜŞSÜN, the implication is that the speaker´s knowledge of the other party waiting for his return is based on what others (3rd parties) told him, not on personal observation.

Hope this helps.

Thanks, AlphaF. The use of these small conjunctions is really difficult to understand for a learner. Imitating native use is even more difficult. Half of the things I thought I knew even turned out wrong. de/da would be worth a thread of its own.

I wish someone who is able to help, and has enough time, would write to me.

I request someone who is able to help, and has enough time, to write to me.

Depends on the context of if "wish" is a request or if its just hopeful thinking. Would this change it in Turkish though?

Thanks for tidying "my all over the place " sentence Mavili. It is actually a request, in other words it is bit softened imperative [command form of a verb] form by adding "lütfen" ......... "yazsın "

So "request" is more appropriate for the sentence.