Yes. Did you then reverse the balloons? There is no guarantee that the one on the plane did not have a leak (presumption). Otherwise, use high quality condoms as the Surgeon General's Office warranties that they are free of leaks.
The other problem with these tests is a change in the barometric pressure. Higher baro, smaller balloon and vice versa. Maybe a better test would be to use a water tube loop mounted vertically and calibrated in inches.
Take a barometric reading when sealed and also the next day and correct the resultant water level reading. This way use can test with both positive and negative pressure.
Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)
Darwinian culling phrase: Watch This!