EVERY airline flight you are on has at least a handful of mobiles, laptops and other electronic kit left in a standby mode or actively on, rather than shut off as aviation regulators and airlines demand. Every flight, in other words, tests the proposition that hardware carried on board by passengers disrupts the aircraft or confuses the crew with false readings from cockpit instruments. And yet airplane electronics, or avionics to use the technical term, do not routinely squawk or fail.

Your correspondent has not himself performed a controlled experiment to confirm his hunch. Instead, he derives the conclusion from two factors. First, as readers certainly know from their own experience and observation, mobiles and laptops are often put into sleep mode, rather than fully powered down. While most mobile operating systems now have an easy-to-access "airplane mode" in which all of a device's radio circuitry is turned off, not all users remember to switch it on before take-off. Many simply press the "power" button, which puts the device to sleep. Computer owners often just shut the lid, which has a similar effect.

In sleep and standby modes, modern electronics go on chirping wirelessly to sort out an available signal. Newer laptops try to find an active Wi-Fi network, while mobiles boost their power to maximum in the hopes of finding a mast. Other personal electronic devices, or PEDs as the airline industry calls them, emit a range of signals that are inevitable byproducts of functioning electronics. (The Federal Aviation Administration, which regulates all matters aeronautic in America, has issued a list of devices that may be used on planes, though airlines may impose further restrictions; the Federal Communications Commission, meanwhile, bars all use of 800 MHz-band mobiles, which sweeps in nearly all modern phones.

The second factor which led Babbage to his conclusion is an interpolation from a widely cited report published in 2006 in IEEE Spectrum, a magazine produced by the Institute of Electrical and Electronics Engineers (IEEE), a trade body which also sets technology standards. Researchers, with the FAA's and airlines' blessing, conducted extensive measurements of in-flight signal activity on 37 commercial flights in 2003. (The other passengers were unaware of the experiment.)

The study found that passengers were using mobile phones at least once per flight, on average, contrary to FCC and FAA regulations. They sometimes even did so during the critical flight phases of take-off and landing. The IEEE article concluded that the potential for interference with satellite-navigation (Sat-Nav) systems used in cockpits to assist with take-offs and landings in particular was a concern. Yet this was not based on data the article's authors collected themselves. Instead, they culled data from an ongoing NASA project in which the space agency collects reports from pilots about any flight anomalies. The IEEE article's authors found a few dozen examples over a decade ending in 2001, and drew its conclusions from this sketchy, anecdotal and non-rigorous source.

In early 2011 a New York Times reporter wrote that in the past decade, there were only ten incidents reported to NASA by pilots that could be pinned on wireless interference. The reporter was handed a confidential file from the international airline trade group that contained an additional 75 anecdotal crew reports over a seven-year period in which PED interference was suspected. In some cases, crew say they asked passengers to turn devices on and off in the main cabin and witnessed errors in the cockpit that correlated. But such results have never been replicated in a controlled setting.

The number of pilot and crew reports may disturb some fliers. But they are puny compared with the sheer volume of flights that take place: nearly 75m carrying over 5 billion passengers in 2010, according to the Airports Council International. Even if the anecdotal reports—retrospective accounts based on observation, not testing—were a hundredfold higher, the claim that PEDs meddle with avionics would remain tenuous.

The IEEE research conducted in 2003 predated the sharp increase in the sale of smartphones. While all new American phones in 2003 had some kind of hardware that allowed satnav-like positioning for locating emergency calls on the ground, the satnav radios in later devices are much more powerful. Such "world-band" smartphones may cycle through five or more cellular frequency bands when looking to latch onto a mobile base station. These mobile phones also include Wi-Fi and Bluetooth, and can be turned into mobile Wi-Fi hotspots on demand.

The IEEE report noted, "Our data and the NASA studies suggest to us that there is a clear and present danger: cellphones can render GPS instrument useless for landings." In the intervening period, the epidemiological spike that was predicted did not materialise. If the scale of problem that the researchers had anticipated were occurring, many flights a day, perhaps hundreds, would experience bad readings in GPS or other gear, especially on smaller planes that rely more on GPS for navigation and landing and lack the same level of electromagnetic shielding as modern commercial planes.

Your correspondent looked into the issue in 2006 for this newspaper, and came away unconvinced then about the results. Of the aviation experts and regulatory authorities he spoke to, none had solid data on problems, but were inclined to err on the side of caution until more information became available. Since then, no further academic research has been published to Babbage's knowledge, and the FAA's advisory body, known as RTCA, last took a comprehensive look at PEDs in 2006.

Nick Bilton, the lead writer of the Bits blog at the New York Times, has begun inveighing against the ban on mobiles and the restriction on use of PEDs below a flight altitude of 3,000 metres (if effect, shortly after takeoff and before landing). In November he posted an item about the lack of hard evidence. He thought that what experts wrote in response lacked rigour (see his witty ripostes to questions, and assertions, by outraged readers). And a few days ago, he visited a contraption called a semi-anechoic chamber at an electromagnetic testing lab to see whether e-readers like Amazon's Kindle produced any measurably suspect emissions. They do not.

Mr Bilton notes that after speaking to the FAA, American Airlines, Boeing and several others, he heard radically different rationales which appear to contradict one another. A point made in a tongue-in-cheek leader this newspaper published in 2006 holds true: if mobile devices were really dangerous they would not be allowed on board at all.