La compañía aérea cuyos vuelos llegan tarde rastreará el bulto.

Cuyos means whose.

In this sentence, cuyos vuelos = whose flights.

A key point is that cuyo links two nouns and shows possession:

• la compañía aérea = the airline
• sus vuelos = its flights

So:

• La compañía aérea cuyos vuelos llegan tarde... means
• The airline whose flights arrive late...

It is more formal than simply rewording the sentence with que.

Because cuyo must agree with the thing possessed, not with the owner.

Here, the possessed thing is vuelos:

• vuelos is masculine plural
• so we use cuyos

Forms:

• cuyo = masculine singular
• cuya = feminine singular
• cuyos = masculine plural
• cuyas = feminine plural

Examples:

• el hombre cuyo coche... = the man whose car...
• la mujer cuya maleta... = the woman whose suitcase...
• la empresa cuyos empleados... = the company whose employees...
• la escuela cuyas aulas... = the school whose classrooms...

Because cuyo already works like a possessive determiner, so it goes directly before the noun.

Correct:

• cuyos vuelos

Not correct:

• cuyos los vuelos
• cuyos sus vuelos

It behaves a bit like my, your, or their in English:

• my flights
• their flights
• whose flights

So in Spanish:

• cuyos vuelos

Rastreará is the simple future of rastrear.

Infinitive:

• rastrear = to track, trace

Future endings for -ar, -er, and -ir verbs are added to the infinitive:

• rastrearé = I will track
• rastrearás = you will track
• rastreará = he/she/it will track

So:

• La compañía aérea ... rastreará el bulto = The airline ... will track the package/bundle

Spanish often uses the simple future where English uses will + verb.

Because Spanish uses llegar tarde to mean to arrive late.

• llegar = to arrive
• tarde = late

So:

• los vuelos llegan tarde = the flights arrive late / the flights are late in arriving

You do not normally say son tarde for this meaning.
Ser is not the verb used for arriving late.

Compare:

• El tren llega tarde. = The train arrives late / is late.
• Siempre llego tarde. = I always arrive late.

Because the subject is vuelos, which is plural.

Inside the relative clause:

• cuyos vuelos llegan tarde the subject of llegan is vuelos

So the verb must agree:

• el vuelo llega tarde = the flight arrives late
• los vuelos llegan tarde = the flights arrive late

Even though the whole sentence starts with la compañía aérea, the verb llegan belongs to vuelos, not to compañía.

Compañía aérea means airline or literally air company.

It is a perfectly correct and common expression. Another very common word is:

• aerolínea = airline

So these are both natural:

• La compañía aérea...
• La aerolínea...

Compañía aérea may sound slightly more formal or descriptive, but both are standard.

Bulto is a fairly general word for a package, bundle, or item of luggage/cargo.

It is less specific than:

• maleta = suitcase
• paquete = package/parcel

So el bulto could refer to some physical item being handled or tracked, especially in transport or shipping contexts.

Depending on context, it might be:

• a parcel
• a bundle
• a piece of luggage
• a bulky item

A learner should notice that bulto is a broader word than maleta.

Because it agrees with compañía, which is feminine.

• la compañía = feminine singular
• so the adjective must also be feminine singular:
• aérea

Compare:

• el transporte aéreo = air transport
• la compañía aérea = the airline company

The ending changes to match the noun:

• aéreo for masculine singular
• aérea for feminine singular

Yes. Since cuyo is often considered a bit formal, learners often prefer a reworded version.

For example:

• La compañía aérea cuyos vuelos llegan tarde rastreará el bulto.

Could be rephrased as:

• La compañía aérea que tiene vuelos que llegan tarde rastreará el bulto.

Or:

• La compañía aérea, cuyos vuelos llegan tarde, rastreará el bulto.
  if you want to make the relative clause more clearly parenthetical in writing.

The version with cuyos is elegant and concise, but many learners find the longer que + tener structure easier at first.

Yes: the middle part is a relative clause inserted after the noun.

Main structure:

• La compañía aérea ... rastreará el bulto. = The airline ... will track the package.

Inserted description:

• cuyos vuelos llegan tarde = whose flights arrive late

So the full sentence is:

• La compañía aérea [cuyos vuelos llegan tarde] rastreará el bulto.

A useful strategy is to identify the main verb first:

• rastreará

Then the subject:

• La compañía aérea

Then treat cuyos vuelos llegan tarde as extra information describing the airline.

That helps make long Spanish noun phrases much easier to understand.