Export sales were also sought, the Romanian Air Force were reportedly considering buying up to 24 aircraft, however, following the loss of one of the prototypes on 7 November 1936 due to a mid-air structural failure, Romania ordered the rival PZL.37 Łoś instead.
It had been hoped that the Polish national flag carrier Polskie Linje Lotnicze LOT would procure the PZL.30, particularly as it had been seeking a replacement to its aging Fokker F.VII fleet at that time.
[1] While the airline did not outwardly indicate interest in the project, Polish aviation authorities opted to sponsor its development in the hope that LOT would change its mind as it neared completion.
[1] This derivative attracted favourable attention not only from industry but also Polish Air Force officers; in late 1933, a special commission selected the design study for further investigation over several rival proposals.
[2] As the detailed design took form, it became clear that the performance of the PZL.30 was unlikely to match that of a more advanced alternative medium bomber already in development at that time, the PZL.37 Łoś.
However, the Department of Aeronautics identified that, as a result of the substantial differences between the Łoś and preceding aircraft, operational conversion would require extensive training, a capacity in which a more affordable auxiliary bomber would likely play a valuable role.
[3] Continuing the PZL.30's development also enabled the project to act as a fallback option in the eventuality that the more advanced bomber encountered insurmountable technical issues.
[3] Despite the PZL.30's development having occurred within virtually the same timeframe as the PZL.37, the performance of the PZL.30 was noticeably inferior to its counterpart, being both slower and possessing a considerably smaller bomb load than the Łoś, yet incurring a similar per unit cost to produce.
[6] The PZL.30 prototype had been initially powered by a pair of American Pratt & Whitney Wasp Junior radial engines, each capable of producing 420 hp.
At the urging of the Department of Aeronautics, the company refitted the aircraft with the more powerful Bristol Pegasus VIII radial engines, sourced from the United Kingdom.
[4] The aircraft was accepted for a limited production run by the LWS state factory in Lublin, for which Ciołkosz was appointed the technical director and project lead.
[8] Comprehensive static testing and other investigative techniques were applied to the design to identify the cause, which was determined to have been the de-lamination of the wing's plywood skin.
[9] To remedy the issue, the wing was redesigned with greater reinforcement, but this measure increased the aircraft's overall weight, which in turn meant that the LWS-6 had a smaller bomb load than expected while other performance areas were also hampered.
[9][Note 1] As one part of several measures explored to improve the aircraft's performance, a modified prototype was produced that featured a double tail fin; it conducted an initial flight near the end of 1937.
[7] Following the fatal loss of the Pegasus-powered prototype on 7 November 1936, which had resulted the deaths of all on board, including two Romanian officers, Romania placed an order for the rival PZL.37 Łoś instead.
The bombardier was accommodated in the aircraft's glazed nose, the position being provisioned with a forward-facing turret armed with twin machine guns that had a distinctive pointed "beard" directly beneath it.
Production model of the Żubr was considered safe aircraft, with good flight characteristics, and only one crashed before the war due to pilot's error, however, without fatal injuries.