interval output format ?

Hello,

Given the following table:

pilotage=# \d vols
           Table "vols"
  Attribute  |   Type   | Modifier
-------------+----------+----------
 jour        | date     |
 modele      | char(20) |
 matricule   | char(20) |
 pilote1     | char(20) |
 pilote2     | char(20) |
 origine     | char(20) |
 destination | char(20) |
 double      | interval |
 comandant   | interval |
 description | text     |
 code        | char(10) |


and the following query:

    pilotage=# select sum(comandant) from vols;
               sum
    --------------------------
     @ 1 day 19 hours 18 mins
    (1 row)

how can I ask postgres  to return

    43:18

instead of

    @ 1 day 19 hours 18 mins

Thanks,
David