Safety recommendations made after 14 servicemen died when a Nimrod aircraft crashed in Afghanistan have not been fully implemented, the MoD has said.
Thirty recommendations were made after the 2006 crash.
The government said 21 were being implemented, three considered and six put "on hold", which the Nimrod base's local MP called "unacceptable".
The inquest into the 14 deaths has heard Nimrods could have been flying in an "unairworthy" state for 37 years.
Westminster SNP leader Angus Robertson, who represents the Nimrod home base of RAF Kinloss, said under the MoD's own rules, for an aircraft to be considered safe, any risk must be reduced to a level that is as low as reasonably practical.
But he said the announcement about the safety recommendations by Defence Secretary Des Browne, which he made in a letter to the Moray MP, showed this had not happened.
The MoD said the report and recommendations, made by defence firm Qinetiq, were part of a more comprehensive safety review that was continuing into the Nimrod air system.
Meanwhile a senior engineer from defence and aerospace firm BAE Systems has told the inquest that his predecessors, who made the Nimrod some 40 years ago, failed to fit a fire protection system on a key area of risk on the aircraft.
The 37-year-old reconnaissance plane exploded just minutes after undergoing air-to-air refuelling in Afghanistan on 2 September 2006, killing all on board.
An RAF Board of Inquiry (BoI) report into the incident concluded that ageing components and a lack of modern fire suppressants were among the "contributory factors" leading to the accident.
It said fuel probably escaped during air-to-air refuelling into a bay on the aircraft either because of a leaking fuel coupling or an overflowing fuel tank.
The Oxford hearing was told on Tuesday that a section of hot air pipe in one of its dry bays was not lagged to protect it from igniting fuel in the event of a leak from a fuel pipe below it.
HOW THE NIMROD CRASHED
1. Nimrod refuels in mid-air
2. Possible fuel over-flow from number one tank
3. Second possible source of leak is pipe couplings behind number seven tank
4. Leaked fuel contacts hot pipe and ignites
5. Fire and smoke alarms triggered in bomb bay and under floor by sensitive wiring
Coroner Andrew Walker said: "What we have here amounts to a serious design flaw, because we could have a single point failure (where just one fault could cause a serious problem)."
BAE's chief Nimrod engineer Martin Breakell agreed, although he stressed that this scenario would be very unlikely.
When asked by the coroner whether he considered the lack of fire suppressant in the dry bay to be a serious failure, he confirmed: "It is a serious failure."
Tom McMichael, head of airworthiness at BAE's Military Air Solutions, added that if the evidence heard was correct, the Nimrod planes had, at the time of the tragedy, been flying in an unairworthy state for 37 years.
The fact that the dry bay was not fitted with a fire-suppressant system meant it should never have been passed fit to fly, he said.
But an "acceptance conference" in August 1968 decided the Nimrod was airworthy.
Following the crash all air-to-air refuelling on the Nimrod fleet was suspended and that suspension remains in force.
In Mr Browne's letter to Mr Robertson, he said that six of the 30 Qinetiq recommendations were "on hold" because they related to air-to-air refuelling.
The Moray MP said: "It is very unsettling that not all safety recommendations have been complied with fully on the Nimrod fleet.
"The secretary of state has assured MPs that Nimrods are safe, however as he makes clear in his letter not all the necessary changes have been made.
"It must be concluded from Des Browne's letter that current risks to the Nimrod aircraft are not 'as low as is reasonably practicable', and this is not acceptable."
The 14 men killed were:
Flight Lieutenant Steven Johnson, 38, from Collingham, Nottinghamshire, Flt Lt Leigh Anthony Mitchelmore, 28, from Bournemouth, Dorset, Flt Lt Gareth Rodney Nicholas, 40, from Redruth, Cornwall, Flt Lt Allan James Squires, 39, from Clatterbridge, Merseyside and Flt Lt Steven Swarbrick, 28, from Liverpool.
Also Flight Sergeant Gary Wayne Andrews, 48, from Tankerton, Kent, Flt Sgt Stephen Beattie, 42, from Dundee, Flt Sgt Gerard Martin Bell, 48, from Newport, Shropshire, and Flt Sgt Adrian Davies, 49, from Amersham, Buckinghamshire, Sergeant Benjamin James Knight, 25, from Bridgwater, Sgt John Joseph Langton, 29,from Liverpool and Sgt Gary Paul Quilliam, 42, from Manchester.
Lance Corporal Oliver Simon Dicketts, of the Parachute Regiment, from Wadhurst and Royal Marine Joseph David Windall, 22, from Hazlemere also died.
The inquest was adjourned until Wednesday.