I am to be at 6 o'clock

[killer man]

cual es el significado cuando se usa el verb to be de esta manera-
i am to be at 6 o´clock
i was to be at 6 o´clock

 

[Angel_Boots]

I am to + infinitive = Debo + infinitive
In other words, it has the same sense as "must", though the phrase you quoted doesn't really make sense without a phrase relating to where, e.g. "I am to be at the hospital at 6 o'clock".

 

[pecosita]

I am supposed to be...
I was supposed to be...

 

[meugeniag]

Debería estar a las 6 en punto.
Se supone que debo estar a las 6 en punto
En teoría, debo estar a las 6 en punto.

 

[zumac]

I am supposed to be...
I was supposed to be...

I agree with Pecosita.

"I am to be" may be corrrect English, but it is very seldom used anymore for the given context.

An option is:
I have to be ...
I had to be ...

Saludos.