Sonic booms: Who foots the bill when buildings go bang?
Could a sonic boom really stop a cow producing milk or a chicken laying an egg?
By Helen BurchellBBC News Urban myths abound when it comes to the damage caused as jets break through the sound barrier, but, in reality you are more likely to lose some plasterwork, a window pane or possibly watch your dry stone wall collapse - if you are unlucky. Figures obtained by the BBC show 17 sonic booms have been acknowledged by the Ministry of Defence (MoD) in the UK since 2009. The explosive sound certainly keeps the emergency services busy reassuring callers that "a bomb has not gone off nearby", but apart from the shock and surprise, exactly how much harm does a sonic boom do? The MoD said 15 claims for damage following a sonic boom have been made in the past five years and a total of £1,844.53 had been paid in compensation. Breaking glass The latest recorded event took place over Peterborough on 5 June, and was also heard in parts of Lincolnshire. The MoD confirmed its Typhoons from RAF Coningsby had been responding to reports a civilian aircraft had lost radio contact with air traffic control. The aircraft were, it said, authorised to go supersonic for "operational reasons". The sonic boom, which released a high-energy shockwave, shattered windows in Peterborough and dislodged roof tiles in Deeping St James. Compensation claims were made against the MoD in both cases, figures released under a Freedom of Information (FoI) request by the BBC, revealed. Sonic booms have been confirmed in the skies above Berwickshire, Powys, Anglesey, Ceredigion, parts of Yorkshire, Northumberland, Norfolk and Cambridgeshire since 2009. 'Startled' animals Damage claims lodged through the MoD's official channels consisted mainly of broken windows to private properties, a car and a greenhouse. Plasterwork in a church in Alnwick in Northumberland was damaged as a result of a sonic boom in 2012, although a claim a boom later that same year had caused a dry stone wall to collapse in Chipping Norton in Oxfordshire was rejected by the MoD. The ministry paid out a total of £1,670.53 in that year. What causes a sonic boom? •When an aircraft approaches the speed of sound (768mph or 1,236km/h), the air in front of the nose of the plane builds up a pressure front because it has "nowhere to escape", said Dr Jim Wild of Lancaster University. •A sonic boom happens when that air "escapes", creating a ripple effect which can be heard on the ground as a loud thunderclap. •It can be heard over such a large area because it moves with the plane, rather like the wake on the bow of a ship spreading out behind the vessel. Of the 15 claims for damage submitted, the MoD settled five and rejected - or "repudiated" - seven. One claim was dropped and two are still active. It might seem the MoD has got off fairly lightly in monetary terms, compared to other cases across the world. Damage caused when a Thunderbird caused a sonic boom over Tucson, Arizona, in April 2012 resulted in damage claims for the US military totalling $22,000, according to the Air Force Times. Again, this was mainly shattered glass, although much research into other potential damage has taken place in the States. Claims animals are adversely affected by the sonic booms seem difficult to prove, however. A number of investigations into the effects on both farmed and wild animals between the 1960s and 1980s concluded they were just "startled" - in much the same way we are when we hear an unexplained "thunderous explosion", which turns out to be a sonic boom. More than 180 dairy cattle herds within a few miles of several US air bases were studied for 12 months with no evidence found of reduced milk production, according to a 1960 study by Parker and Bayley. The milk yield of dairy cows in an area of frequent sonic booms, Edwards Air Force Base in California, was found to be "similar to the yield of control dairy cows", according to further research carried out by Casady and Lehmann in 1967. 'Meteorological conditions' Two decades later, a series of investigations published by the National Ecology Research Center into the effects of sonic booms and simulated sonic booms on several species, confirmed the "startle reaction". When exposed to a simulated sonic boom, a sea lion reportedly "left the beach and went into the surf", it was noted. The effects of sonic booms have even been monitored on tortoises by one researcher. It found no significant increase in the animals' heart rate or metabolism. So, while animals seem relatively unfazed by sonic booms it seems likely the occasional window pane in the UK will continue to shatter in the future. An MoD spokesman said: "Supersonic training is prohibited overland in the UK for both RAF and USAF fast jet crews. "The majority of incidents where supersonic booms were heard would either have been aircraft completing training over the North Sea, where meteorological conditions led to the sound travelling overland, or RAF Quick Reaction Alert aircraft responding to intercept unidentified aircraft. "It is very rare for accidental supersonic flight during operational training overland, and we apologise for any inconvenience caused when this happens." Meanwhile, people in Anglesey and Lincolnshire are still waiting to find out whether their own broken windows and dislodged roof tiles will be deemed a genuine victim of confirmed sonic booms earlier this year.