When we first produce the Melody/Instrumental parts we take it from the lead vocal part and transpose it, if necessary, into a generalised range. We are aware that there may occassions when notes fall outside the range of some instruments.
As an example, a low A is quite easy to play on a Bb Trumpet but it falls below the lowest note of the Saxophone. Likewise, a high E can be really difficult on trumpet but it is not much of a problem for a Bb Clarinet.
As you can see there will probably be occasions when notes do exceed the range of your instrument. We suggest taking a common sense approach and transpose any of those phrases where note(s) go out of range.