def createId(df1, dest_col, cols):
    """

    Append flight IDs to the input table (usually the FSU table).

    Parameters:

       df1 (pandas.DataFrame) : input dataframe to enhance with flight identifiers
       dest_col (string) base name of the identifier column
       cols (list(string)) : columns from which to form the identifier

    Return:
       A dataframe with one additional identifier column.

    The original input remains intact. The number of rows in the returned dataframe
    is identical to the number of rows in the input dataframe.

    """
    df = df1.copy()
    df[dest_col] = df[cols[0]]
    for i in range(1,len(cols)):
        df[dest_col] += df[cols[i]]
    return df