An airborne ultrasonic testing apparatus for inspecting a seal of a package in a gaseous environment, comprising: a first transmitting transducer having an ultrasound energy emitting portion; a first receiving transducer having an ultrasound energy sensing portion; a second transmitting transducer having an ultrasound energy emitting portion; a second receiving transducer having an ultrasound energy sensing portion; a seal-receiving slot defined between the first and second transmitting transducers (12, 13) and the first and second receiving transducers (14, 15), the seal-receiving slot having a length for receiving therein a seal portion of a package to be tested, wherein the first and second transmitting transducers are configured to emit ultrasound energy towards the respective first and second receiving transducers at an oblique angle with respect to a longitudinal axis of the slot, wherein the first transmitting transducer emits ultrasound energy at an angle which is inverse of the angle of the ultrasound energy emitted by the second transmitting transducer with respect to a perpendicular to said longitudinal axis; an ultrasound frequency generator in communication with the first and second transmitting transducers; a computer analyzer in communication with the first and second receiving transducers (14, 15), the analyzer providing an indication of integrity of a seal portion of a package to be tested based on a combination of measurements, wherein a measurement from the first receiving transducer is combined with a measurement from the second receiving transducer to produce a summary test result of the two measurements so as to eliminate systematic variation and produce a smooth measurement line; and a controller in communication with the ultrasound frequency generator for controlling the actuation of the ultrasound frequency generator during a testing event. a first transmitting transducer having an ultrasound energy emitting portion; a first receiving transducer having an ultrasound energy sensing portion; a second transmitting transducer having an ultrasound energy emitting portion; a second receiving transducer having an ultrasound energy sensing portion; a seal-receiving slot defined between the first and second transmitting transducers (12, 13) and the first and second receiving transducers (14, 15), the seal-receiving slot having a length for receiving therein a seal portion of a package to be tested, wherein the first and second transmitting transducers are configured to emit ultrasound energy towards the respective first and second receiving transducers at an oblique angle with respect to a longitudinal axis of the slot, wherein the first transmitting transducer emits ultrasound energy at an angle which is inverse of the angle of the ultrasound energy emitted by the second transmitting transducer with respect to a perpendicular to said longitudinal axis; an ultrasound frequency generator in communication with the first and second transmitting transducers; a computer analyzer in communication with the first and second receiving transducers (14, 15), the analyzer providing an indication of integrity of a seal portion of a package to be tested based on a combination of measurements, wherein a measurement from the first receiving transducer is combined with a measurement from the second receiving transducer to produce a summary test result of the two measurements so as to eliminate systematic variation and produce a smooth measurement line; and a controller in communication with the ultrasound frequency generator for controlling the actuation of the ultrasound frequency generator during a testing event.