Knox Martin Air post issue. Yvert PA1 on cover tied by "BARRANQUILLA" cds, June 18 to Punto Colombia with arrival on observe.Kessler guarantee & 2002 PF photo certificate. Yvert Euros 2,300 for a single off-cover. The item "COLOMBIA 1919 KNOX MARTIN AIR Sc C1 Yv PA1 ON COVER PF CERTIFICATE F, VF 2,300++" is in sale since Monday, November 20, 2017. This item is in the category "Stamps\Latin America\Colombia". The seller is "victorgg" and is located in Buenos Aires. This item can be shipped worldwide.