Given the task definition and input, reply with output. In this task, you need to remove all words of a given length in the sentence. The number of letters in a word determine its length, for example, the length of the word "apple" is 5.

Sentence: 'a qantas spirit of australia airplane flying in a clear blue sky'. Remove all words of length '6' in the given sentence.

a of australia airplane in a clear blue sky