After an apparently near-impeccable year for airline safety in 2017, the traditional accidents are returning. In the last week a Russian carrier has fatally lost a twinjet, and an Iranian airline a twin turboprop.

It would be closer to the truth to say these accidents – or at least the risk they represent – never went away, it’s just that a year is too short a time in which to measure the true safety performance of an industry.

The previous story in this blog sequence investigated the part that luck plays in airline safety, and it concluded that it still plays an unacceptably big part in an industry that confidently tells its passengers it has high standards.

The Russian loss involved a Saratov Airlines Antonov An-148 regional twinjet. It had taken off from Moscow Domodedovo airport in snow, bound eastward for Orsk, but after about 6min its climb became a rapid descent and it hit fields at high speed.

Early data from the investigation suggests the trigger for the fatal sequence of events was a disparity in airspeed indicator readings, probably caused by ice build-up in the external sensor because its heater had failed. The crew saw the disparity developing between the airspeed indicators and tripped out the autopilot, but failed in their attempts to fly the aircraft successfully relying on instruments that included misleading  airspeed data.

Less detail is known about the Iran Aseman Airlines ATR72, but it was on a flight from Tehran to Yasouj among Iran’s south-western mountains. The destination is cradled in a valley, and the aircraft hit mountains about 30km north of the city in its early descent. The mountainous terrain was under complete cloud cover and snow.

The Saratov case provides more evidence of pilots’ unpreparedness for “limited panel” instrument flying. Air France 447 was the most famous example of pilot inability to cope with instrument flying when the airspeed sensors were temporarily compromised by ice, but the final report revealed that there had been six other recorded occasions in the same aircraft type (A330) where pilots had coped successfully with unreliable airspeed readings.

Airline recurrent trainers need to go back to basics with instrument flying, because it is increasingly clear many pilots all over the world are losing this crucial skill.

Loss of reliable airspeed information is unsettling, and it usually causes the autopilot to trip out, so airlines should ensure their pilots are able to cope with this situation.

In stable flight, whether level, climbing or descending, airspeed is a product of engine power and pitch attitude. All pilots with time on a particular type should know approximately what power will produce the performance they want.

So if they become aware that airspeed indications are compromised, it makes sense to adopt straight and level flight (if at a safe altitude) while sorting out a Plan B. That way the attitude is stable, and if the pilot selects the power setting that will produce a safe airspeed, all is well. However unsettling it is to see an airspeed reading that is clearly wrong, and which would be dangerous if true, it is a plain fact that the correct pitch attitude for S & L flight plus the correct power setting will produce the correct airspeed.

In the case of the Iran Aseman ATR72 the cause of the crash isn’t known yet, but there was no emergency call and that range of mountains contains many aircraft wrecks. If it turns out to be a classic case of CFIT (controlled flight into terrain), the issue will be one of three-dimensional navigation on instruments. Yes, such approaches are demanding, but these procedures should be the lifeblood of crews working for Iranian domestic carriers, for whom approaches into airports surrounded by mountains is their daily work.

These airlines – and others – have to ask themselves what is missing in their pilots’ skills, and why these skills are missing at all. Finally, they have to ask what they need to do to replace skills that have lapsed.

If the investigators’ final verdict is that pilot error was a factor in these accidents, the fault lies squarely with the carriers for failing to ensure, in their recurrent training regime, that their pilots have the living skills their passengers have a right to expect.

And again, if that verdict were to be delivered by the investigators, the airlines should worry about whether their existing crews could fail in the same way tomorrow.