The '250A' advanced development project with slightly uprated AL-7F-1 engines was completed in October 1955 and approved in early 1956. Overall the interceptor's performance was slightly reduced while the flight parameters for the targets had been revised to 19,500m (63,976ft) altitude and 1,200km/h (746mph) speed. In the meantime the original '250' prototype was completed on 16th June 1956, work on it having continued because Lavochkin had decided to use the aircraft for preliminary flight tests and as a systems testbed. The AL-7F-1 was also not yet available and so the '250' was fitted with standard AL-7Fs rated at 67.6kN (15,2101b). Preflight ground testing went well and on 16th July the '250' made its first 'flight', except that two seconds after getting airborne it banked several degrees to starboard and then started pitching and rolling. The pilot opted for an immediate landing, after which the aircraft caught fire and was written off. The cause was the control system, which had to be redesigned.
When completed in the spring of 1957 the first '250A' had the modified control system and also AL-7Fs because the AL-7F-1 was still unavailable. There were numerous other changes including intakes placed further forward and differences around the jetpipe, which to a degree had altered the interceptor's appearance. The first '250A' flew on 12th July 1957 but was to become another loss, written off in a landing accident on 28th November. This time pilot visibility was the problem and so the third aircraft (that is, the second '250A') had the nose ahead of the windshield angled down by 6° (right from the mock-up stage several pilots had declared that the long nose would give problems with external vision). This aircraft flew in July 1958, still powered by AL-7Fs (and without working afterburners), which meant that the flight envelope could not be explored in full.
The first three '250' and '250A' prototypes made their maiden flights at roughly twelvemonth intervals and the long delays being experienced with the engines put the programme way behind schedule. A K-15M radar was finally fitted to the fourth prototype while the fifth machine had a complete weapons and avionics suite. At last, in May 1958 all of the components of the K-15 weapons system - aircraft, missiles and radar - were ready for testing, but it was too late. The delays had left their mark and the Commander-in-Chief of the Soviet Air Force, Marshal Konstantin A Vershinin, voiced criticism of the aircraft's time schedule and added that the whole system was becoming obsolete. As a result, in July 1959 the government issued a directive cancelling the K-15 weapons system as a whole, including the '275' missile. By now work was also progressing on the Su-9 and the competing Tu-28-80 which would more than fill the gap left by the disappearance of the '250A'.
Even allowing for the development problems and the fact it did not receive the engines it needed, Lavochkin's interceptor exhibited a disappointing performance. Top speed was just 1,080km/h (671 mph) instead of the desired 1,610km/h (1,001mph), service ceiling 13,300m (43,635ft) instead of around 17,000m (55,774ft) and time required to reach 12,000m (39,370ft) 5.4 minutes instead of around half that. As an Aircraft Design Bureau this was Lavochkin's swan song because the Soviet government now decided that the OKB should switch to being a specialist missile manufacturer - it was never again to be involved with fighter design although it did get involved with spacecraft. However, the '250VK-15 design effort was not wasted because much of the data and experience gained with it was transferred to the Tupolev OKB to help with the 'Aircraft 128' heavy interceptor. Only one '250A' survives today which is held in the Monino Museum and no Westem codename was allocated to the type.