Learn Turkish: Motoru bozulan uçağın irtifa kaybedeceğini biliyoruz. - We know that the airplane whose engine broke down will lose altitude.

It is the subject of the embedded clause 'that the airplane will lose altitude.' In Turkish, when a clause is nominalized using suffixes like -DIk or -(y)AcAk, its subject takes the genitive case (-In). The verb then takes a matching possessive suffix. You can think of it literally as 'We know the airplane's future losing of altitude.'

How does motoru bozulan translate to 'whose engine broke down'?

Turkish doesn't have a single word for 'whose.' Instead, it uses a subject relative clause (-An) combined with a possessed noun. Motoru means 'its engine,' and bozulan means 'that broke down.' Placed before uçağın, the whole phrase motoru bozulan uçağın literally means 'the airplane that its engine broke down.'

Why is there an accusative suffix (-ni) at the end of kaybedeceğini?

The main verb of the sentence is biliyoruz (we know). The accusative case marks the entire embedded clause (uçağın irtifa kaybedeceği) as the specific direct object of the verb 'to know.' It tells us exactly what is being known.

Can you break down the stack of suffixes on kaybedeceğini?