The report concludes that the organisers were unaware of the pilot's display manoeuvres. It says the Civil Aviation Authority (CAA) missed an opportunity to check the pilot's competence.
On 22 August 2015 pilot Andy Hill performed a stunt involving looping and rolling a Hawker Hunter (G-BXFI) jet. The aircraft failed to resume level flight after the manoeuvre and crashed into the A27 westbound carriageway. Eleven people were fatally injured and 16 were hurt. The aircraft was destroyed but Hill survived.
AAIB Bulletin S1/2016 Special draws on investigations by the board and the Health and Safety Laboratory (HSL).
The AAIB found that the risk assessment document for the 2015 Shoreham show did not consider the hazards posed by each different type of aircraft at the event, where these hazards would occur and who would be exposed to them. Assessments, according to the Civil Aviation Publication (CAP) 403, should "identify the hazards associated with activities contributing to the event, where the activities are carried out and how they will be undertaken."
There was no evidence of an attempt to consider either a hierarchy of protection or control, the report says and it calls on the Civil Aviation Authority (CAA) to publish guidance to help inform show risk assessments.
The HSL reviewed the Shoreham organisers' assessment and concluded: "It is not clear that those who assessed the risks and recorded the assessment had a full understanding of the purpose of the risk assessment".
An enhanced risk assessment carried out by the CAA after the crash, which looked into nearby infrastructure and transport links, identified there was a risk to users of major roads near the site. The assessment recommended "active traffic management" to keep vehicles flowing and avoid congestion. The report states this was in fact an ineffective method to mitigate the risk because, though traffic management was in place on the day of the accident, the plane hit several vehicles.
The AAIB has recommended that the CAA "introduces a process to ensure that the organisers of flying displays have conducted suitable and sufficient risk assessments before a permission to hold such displays is granted under Article 162 of the Air Navigation Order".
The report says that the Shoreham show's flying display director (FDD), though an experienced pilot, was unable to recognise the hazards associated with the display plan or identify who would be exposed to them, or to what extent, because he received no previous information about the pilot's routine or the ground area it would cover.
The AIIB suggests the UK could learn from other countries' display regulations. In the US, for example, the Federal Aviation Administration attends every authorised air display. Last year the CAA attended just 18 of the 254 displays it permitted.
In Canada, display organisers must provide a "sequential list of all the manoeuvres to be flown by the performer" at least 10 days before a display. These include the distance of each manoeuvre from spectator areas, and the directions of flight relative to the spectator areas.
The written CAA permission FDDs must obtain before a show under Article 162 of the Air Navigation Order places responsibilities on both them and the pilots.
But after reviewing recent airshows, the report says: "In some cases the CAA, in issuing an Article 162 permission, changed the position or orientation of a display line. There was no evidence, in these cases, that the CAA or the FDDs for those events had assessed how this might change the risks or who was ultimately responsible for the safety of the chosen line. This introduced the potential for confusion over who owned the risk and to diffuse responsibility, so different parties each assumed the other was reponsible for controlling the risks.
The report also reveals that, while carrying out a display in 2014 in another aircraft type, pilot Andy Hill was stopped by the FDD due to concerns over one of his stunts.
It says: "Following an informal discussion with the pilot later that day the CAA took no further action and did not formally record the occurrence. The occurrence was not otherwise investigated and was not reported to the AAIB -¦ The occurrence could have provided an opportunity to explore the pilot's continued competence."
The report also suggests new rules to avoid conflicts of interest after investigations discovered that a G-BXFI pilot in 2014 was "evaluated in relation to his Display Authorisation by a member of the same display team".
This was also the case for the pilot involved in another fatal accident last year at an airshow at Oulton Park, Cheshire.
The AAIB will publish its full report on the crash later in the year.