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