Learn Hardcore Turkish: Otobüs kalkmak üzereyken ona el salladık. - When the bus was about to depart, we waved to her.

kalk-mak = to leave/depart (infinitive)
üzere = on the verge of / about to
-(y)ken = while/when (the buffer y appears because üzere ends with a vowel)

So kalkmak üzereyken = “when it was on the verge of leaving.”

Why is it kalkmak (infinitive) and not a conjugated form?

Because üzere takes the verb in the infinitive (-mak/-mek). Examples:

Film başlamak üzere = The movie is about to start.
Otobüs kalkmak üzereyken = While the bus was about to leave.

Can I use kalkarken or kalkıyorken instead of kalkmak üzereyken?

They’re close but not the same:

kalkmak üzereyken: right before departure (imminent, hasn’t really started).
kalkarken / kalkıyorken: during the process of departing (it has started). Alternatives: kalkmadan (hemen) önce = just before it left; kalktıktan sonra = after it left.

What does ona do here? Why not onu?

Ona is dative “to him/her/it.” The idiom el sallamak (to wave at someone) takes the dative case for the target. Onu is accusative and would be wrong here. Similar dative-governing verbs: bakmak (to look at), gülmek (to laugh at), bağırmak (to shout at).

Does ona refer to a person or to the bus?

By itself, ona can mean “to him/her/it.” Contextually, you usually wave to a person. If you literally mean the bus, say otobüse el salladık. To be explicit about a person on the bus: Otobüsteki adama/kadına el salladık.

Why is there no biz? How do we know it’s “we waved”?

Turkish verbs carry person/number. salladık has the past tense -DI and first-person plural -k, so it already means “we waved.” The subject pronoun biz is optional and used for emphasis.

How is salladık formed?

From the root salla- (to shake/wave) + past -DI (with vowel harmony → -dı) + 1st pl -k:

salla-dı-k = we waved Other forms: salladım (I waved), salladı (he/she waved), salladılar (they waved).

Why do we say el sallamak? Can I just say salladık?

The idiomatic way to say “to wave (at someone)” is el sallamak (“to wave a hand”). Sallamak alone means “to shake/swing/wag,” not necessarily “wave (hello).” So you need el in this idiom.

Should it be elimizi (our hand) instead of just el?

No. El sallamak is a fixed expression and doesn’t normally take a possessive. You can say elimi/elimizi for emphasis, but the neutral, idiomatic form is simply el sallamak.

Should there be a comma after …üzereyken?

Often a comma is used for clarity when the adverbial clause comes first: Otobüs kalkmak üzereyken, ona el salladık. It’s style-dependent; without a comma is also seen.

Can üzere be used as a main predicate without -yken?

Yes:

Otobüs kalkmak üzere. = The bus is about to leave.
Past: Otobüs kalkmak üzereydi. Your sentence compresses this into a time clause with -yken.

Does üzere have another meaning besides “about to”?

Yes, it also means “in order to/for the purpose of”:

Toplantı yapmak üzere toplandık. = We gathered in order to hold a meeting. In your sentence, it’s the “about to” meaning.

Can I say kalkacakken instead of kalkmak üzereyken?

Yes: Otobüs kalkacakken ona el salladık. It means “just as the bus was going to leave.” kalkmak üzereyken often sounds a bit more formal; kalkacakken is common and natural. You can add tam for emphasis: tam kalkmak üzereyken.

How flexible is the word order? Can I move ona?

Turkish word order is flexible for focus, but keep the idiom el sallamak together. Variants:

Otobüs kalkmak üzereyken ona el salladık. (neutral)
Ona, otobüs kalkmak üzereyken el salladık. (focus on “to him/her”) Putting words between el and salladık is unusual unless you’re emphasizing something specific.

What are alternatives to kalkmak for vehicles?

hareket etmek = to depart/move: Otobüs hareket etmek üzereyken…
ayrılmak = to leave (more general): Otobüs ayrılmak üzereyken… For planes, kalkmak also means “to take off.”

Is it ever written o’na with an apostrophe?

No. Ona is a common pronoun and never takes an apostrophe. Apostrophes in Turkish attach suffixes to proper names: Ankara’ya, Ayşe’ye.

Any quick pronunciation tips for otobüs and üzereyken?

ü is a front rounded vowel (like French “u” in “tu”).
otobüs: o-to-büs (stress typically near the end).
üzereyken: ü-ze-re-y-ken (smoothly link the vowel with the buffer y in -yken).