def METHOD_NAME(number: int, prefix: str = "a") -> str:
    """
    Creates an American ICAO number composed from the prefix ('a' for USA)
    and from the given number.
    The output is an hexadecimal of length 6 starting with the suffix
    >>> create_icao(11)
    'a0000b'
    >>> create_icao(915399)
    'adf7c7'
    >>> create_icao(999999)
    Traceback (most recent call last):
        ...
    RuntimeError: Invalid value, must be below 0xdf7c7 for N99999
    """
    if number > 0xDF7C7:
        raise RuntimeError("Invalid value, must be below 0xdf7c7 for N99999")
    return prefix + hex(number)[2:].rjust(5, "0")