حالما يعلن موظف المحطة عن موعد الوصول، أقرأ لوحة المغادرة.

حالما means as soon as.

In this sentence, it introduces an action that happens immediately after another action:

• حالما يعلن موظف المحطة عن موعد الوصول، أقرأ لوحة المغادرة.
• As soon as the station employee announces the arrival time, I read the departure board.

A useful point: حالما is a fixed expression in Modern Standard Arabic. Learners do not usually need to analyze it word by word at first; it is best learned as one unit meaning as soon as.

In Arabic, the present tense often appears after words like حالما when talking about a future or repeated action.

So حالما يعلن literally looks like as soon as he announces, but depending on context it can mean:

• As soon as he announces
• Whenever he announces
• Once he announces

Arabic commonly uses the present tense in this kind of time clause, even where English might also use a present tense. The second verb, أقرأ, is also in the present tense, which makes the whole sentence feel like a habitual action or a general sequence.

Because in Arabic, when the verb comes before the subject, the verb is normally singular.

Here the order is:

• يعلن موظف المحطة
• literally: announces the station employee

Since موظف المحطة is singular, يعلن is singular masculine.

This is normal Arabic word order:

• verb + subject

If the subject were placed first, you would more often get full agreement:

• موظف المحطة يعلن...

But in the original sentence, the verb-first structure is the standard pattern.

موظف means employee or staff member.
المحطة means the station.

Together, موظف المحطة literally means:

• employee of the station
• more naturally in English: the station employee or a station employee

This is an iḍāfa construction, often called a possessive or genitive construction:

• موظف = employee
• المحطة = the station
• موظف المحطة = station employee / employee of the station

Notice that the first word in an iḍāfa does not take الـ.

This is another iḍāfa construction.

• موعد = time, appointment, schedule
• الوصول = the arrival / arrival

Together:

• موعد الوصول = the arrival time

In Arabic, an iḍāfa becomes definite if the second noun is definite. Since الوصول has الـ, the whole phrase is definite.

So even though موعد has no الـ, موعد الوصول still means the arrival time, not just an arrival time.

In Arabic, the verb أعلن / يعلن often takes the preposition عن when it means announce or declare something.

So:

• يعلن عن موعد الوصول
• he announces the arrival time

Literally, you can think of it as announce about something, although that is not how we would normally say it in English.

This is just a verb-preposition pattern that learners need to remember:

• أعلن عن = to announce

Literally, it means:

• لوحة = board, panel, sign
• المغادرة = departure

So لوحة المغادرة means:

• the departure board

This is also an iḍāfa construction:

• لوحة المغادرة
• board of departure
• natural English: departure board

At a station or airport, this is the board showing departures.

المغادرة is a very common formal word for departure in travel contexts, especially in Modern Standard Arabic.

You may also meet other words in related contexts, but مغادرة is extremely standard for:

• departure boards
• departure times
• official announcements

So لوحة المغادرة is a natural MSA phrase.

أقرأ is the present tense: I read / I am reading / I will read, depending on context.

Arabic often uses the plain present tense for:

• habits
• general truths
• repeated actions
• sequences triggered by another event

So in this sentence, أقرأ can suggest:

• I read the departure board whenever that happens
• or I read the departure board as soon as that happens

If the speaker wanted to emphasize a specific future action, سأقرأ could be possible in another context, but أقرأ is perfectly normal here.

Most naturally, it sounds like a habitual or general action:

• As soon as the station employee announces the arrival time, I read the departure board.

That sounds like something the speaker usually does.

However, Arabic present-tense sentences like this can sometimes also be understood more broadly depending on context. Without extra context, the habitual reading is the most natural one.

With full case endings, it would be:

حالما يُعلِنُ موظفُ المحطةِ عن موعدِ الوصولِ، أقرأُ لوحةَ المغادرةِ.

Here is why:

• يُعلِنُ: present tense, indicative
• موظفُ: subject of the verb, so nominative
• المحطةِ: second term of iḍāfa, so genitive
• عن موعدِ: after عن, genitive
• الوصولِ: second term of iḍāfa, genitive
• أقرأُ: present tense, indicative
• لوحةَ: direct object, accusative
• المغادرةِ: second term of iḍāfa, genitive

In normal Arabic writing, these endings are usually not written, but they are still understood grammatically.

They are similar, but not identical.

• عندما = when
• حالما = as soon as

So حالما is more immediate. It suggests that the second action happens right after the first one.

Compare:

• عندما يعلن موظف المحطة... = When the station employee announces...
• حالما يعلن موظف المحطة... = As soon as the station employee announces...

So حالما is the stronger, more immediate expression.

The comma separates the time clause from the main clause:

• حالما يعلن موظف المحطة عن موعد الوصول = time clause
• أقرأ لوحة المغادرة = main clause

This works much like English punctuation in a sentence such as:

• As soon as the station employee announces the arrival time, I read the departure board.

The comma helps readability, especially when the sentence begins with the time expression.