Editing Vickers Valiant (section)

===Fatigue failures and retirement===
In 1956, Vickers had performed a series of low level tests in WZ383 to assess the type for low level flight at high speed. Several modifications to the aircraft were made, including a metal radome, debris guards on the two inboard engines, and after six flights the aileron and elevator artificial feel was reduced by 50%. Pilots reported problems with cabin heating and condensation that would need remedying. The aircraft was fitted with data recording equipment and these data were used by Vickers to estimate the remaining safe life of the type under these flying conditions. Initially a safe life of 75 hours was recommended, which became "the real figure might be less than 200 hours".<ref>Morgan p. 66-68</ref> The number of hours flown by each Valiant in a year was an operational issue for the RAF.<ref>Valiant Units of the Cold War, Brookes p. 88.</ref>

[[File:15 Vickers Valiant WZ397 (15216077444).jpg|thumb|left|Vickers Valiant on display]]
Later the [[Royal Aircraft Establishment|RAE]] ran a similar series of tests that more closely resembled actual operational conditions including low level and taxiing; the corresponding report published in 1958 produced data that could be used to get a better grasp on which flight conditions produced the most damage, and enable a better projection of the future life span for the type.<ref>[http://naca.central.cranfield.ac.uk/reports/arc/cp/0521.pdf "Fatigue Loadings in Flight-Loads in the Nose Undercarriage and Wing of a Valiant."] E.W. Wells, ARC C.P. No. 521.</ref>

In May 1957 ''Flight'' reported an "incident at Boscombe Down, when the wing rear spar cracked after a rocket-assisted takeoff at overload weight (the reason for the rocket-assistance)"<ref>''Flight'' 17 May 1957, p. 651</ref> This aircraft was the second prototype WB 215 and had not been modified with the production fix for the known weakness in the rear spar;<ref>Properly to Test Book One "The Early Years",Noble 2003,{{ISBN|0 9544507 1 X}},p.96</ref> the aircraft was subsequently broken up for wing fatigue testing after it had flown 489 hours.<ref>Morgan p. 44 & p. 89.</ref>

After years of front-line service, in July 1964, a cracked spar was found in one of the three Valiants (either WZ394 – Wynne, or WZ389 – Morgan) on Operation Pontifex.<ref>Wynn p. 469.</ref> This was followed on 6 August by a failure of the starboard wing rear spar at 30,000&nbsp;ft,<ref>Brookes, Victor Units of the Cold War, p. 67.</ref> in WP217, an OCU aircraft from Gaydon captained by Flight Lieutenant "Taffy" Foreman. The aircraft landed back at Gaydon but without flap deployment because damage to the starboard rear spar caused the flap rollers to come out of their guides so that the flap would not lower on that side. Later inspection of the aircraft also showed the fuselage skin below the starboard inner plane had buckled, popping the rivets; the engine door had cracked and the rivets had been pulled and the skin buckled on the top surface of the mainplane between the two engines.<ref name = "darling 39 40">Darling 2012, pp. 39–40.</ref> Both of these aircraft were PR variants.<ref>Morgan, App 2, Individual Valiant Histories pp. 89–94.</ref>

Inspections of the entire fleet showed that the wing spars were suffering from fatigue at between 35% and 75% of the assessed safe fatigue life, probably due to low level turbulence.<ref name = "darling 40">Darling 2012, p. 40.</ref> After this inspection, the aircraft were divided into three categories, Cat A aircraft continuing to fly, Cat B to fly to a repair base, and Cat C requiring repair before flying again. The tanker squadrons had the highest proportion of Cat A aircraft because their role had been mainly at high level.<ref name = "darling 40"/> This also caused the methods of assessing fatigue lives to be reviewed.<ref>Wynn 1996, p. 465.</ref> By the time the type was scrapped, only about 50 aircraft were still in service; the rest had been slowly accumulating at various RAF Maintenance Units designated as "Non effective Aircraft".<ref>Morgan App2, pp. 89–94.</ref>

Initially there was no question of retiring the type, or even a majority of affected aircraft. Repairs were actively taking place at Valiant bases such as Marham using working parties from Vickers plus RAF technicians from the base.  In January 1965, the Wilson government with [[Denis Healey]] as [[Secretary of State for Defence]] decided that the expense of the repairs could not be justified, given the short operational life left to the Valiant, and the fleet was permanently grounded as of 26 January 1965.<ref>[https://news.google.com/newspapers?id=wGNAAAAAIBAJ&sjid=nKMMAAAAIBAJ&pg=5895,4007485&dq=vickers+valiant&hl=en "Valiants to be Scrapped."] ''Glasgow Herald'', 27 January 1965.</ref> The QRA alert that had been in place for [[SACEUR]] was maintained until the final grounding.<ref>Wynn 1996, pp. 464–471, 500.</ref> When asked to make a statement regarding the Valiant's scrapping in the [[House of Commons of the United Kingdom|House of Commons]], Denis Healey stated that it "was not in any way connected with low-level flying" and that the "last Government took the decision to continue operating the Valiant force for another four years after its planned fatigue life was complete".<ref>{{citation |url=https://api.parliament.uk/historic-hansard/commons/1965/feb/01/royal-air-force-valiant-aircraft#column_725|title=ROYAL AIR FORCE (VALIANT AIRCRAFT) |work=[[Hansard|Parliamentary Debates (Hansard)]] |date=1 February 1965 |volume=705|at=cc723-7}}</ref>

Aviation author Barry Jones commented in his book that: "A question has to be asked. For two years before the demise of the Valiant, Handley Page at Radlett had 100 [[Handley Page Hastings|Hastings]] go through their shops. They were completely dismantled and rebuilt, having DTD683 components removed and replaced by new alloy sections. What was so special about the Hastings and why was the Valiant not treated similarly? Perhaps we will know one day – but I doubt it."<ref>"V-Bombers" Barry Jones p. 117.</ref> A ''Flight'' report about the scrapping states "Fatigue affected all Valiants ... not only those that had been used for some low flying".<ref>{{citation |url=http://www.flightglobal.com/pdfarchive/view/1965/1965%20-%200310.html|title=End of the Valiants|work=Flight International |date=4 February 1965 |page=184}}</ref>

On 9 December 1964, the last Valiant tanker sortie in XD812 of 214 Squadron was refuelling Lightning aircraft over the North Sea and was recalled to land back at Marham before the scheduled exercise was completed. On the same day, the last Valiant bomber sortie was carried out by XD818.{{#tag:ref|XD818 was also the aircraft which had dropped nuclear weapons during [[Operation Grapple]].|group=N}}