Sonic Clutter in the Cockpit
Sound design can have life-and-death consequences. When will airplane manufacturers take it seriously?
This article first appeared on LinkedIn last year.
We have another example of cockpit’s sonic environment interfering with safe operations of a passenger airplane. Fortunately, in this instance, everything turned out for the best-no accident, no injury, no loss of life. But we know from recent history that this is not always the case.
Yesterday, the Safety Investigation Authority of Finland (SIAF) released a report about an incident at Helsinki’s Vantaa Airport on January 18, 2019. The incident concerns two airplanes that were landing in succession on one of the airport’s runways. A Turkish Airways plane landed on the runway, slowed, and began to exit to a taxiway. The air traffic controller had already issued landing clearance for the following airplane, a Norwegian Boeing 737-MAX. Such clearance is standard procedure when a controller expects a plane to exit the runway at a particular rate; this procedure allows airports to operate efficiently.
In this instance, however, the Turkish flight exited the runway slower than the controller expected. Because the Turkish plane had not yet reached the required position away from the runway, the controller contacted the following Norwegian plane to cancel landing clearance. The plane should have “gone around”-climbed back to a few thousand feet and positioned again to land-but in fact, the plane continued its landing sequence.
It’s easy to see how such an incident can go horribly wrong. Spacing requirements exist to prevent collisions between airplanes; when these requirements are ignored, planes and their passengers are put at grave risk.
So why did this happen? The controller in Helsinki realized the problem in sufficient time to issue a go-around instruction to the Norwegian flight, and yet the Norwegian plane continued to land. The controller acted appropriately to maintain safe distance between planes, so why did the Norwegian crew ignore the go-around instruction?
The answer is: they didn’t. They simply did not hear the instruction from the controller. The SIAF report notes:
“They did not hear the go-around instruction because it was masked by automated height callouts. Since controllers and pilots communicate verbally, messages can be distorted and blanked by automated callouts. The sole way of transmitting a go-around instruction is voice communication on a radio frequency. Immediate action instructions could be made more distinguishable from other communications for example by inserting an audio tone at the beginning of the message. This would be fairly straightforward technically, but no such solutions are used in aeronautical radio communications.”
The acoustic ecosystem of the cockpit masked the controller’s instruction. Unaware that landing clearance had been revoked, the Norwegian crew continued to land as planned. This incident was minor, but it sheds light on a potentially life-threatening hazard. What would happen if the Norwegian crew had missed a major warning or instruction from the controller because their airplane did not allow them to hear it?
A History of Sonic Neglect
Unfortunately, the air transport industry does not have a good record of using sonic information safely and productively. The Federal Aviation Administration issued a report earlier this year about the crash of a 737-MAX operated by Lion Air. In it, they observed,
“While Boeing considered the possibility of uncommanded MCAS operation as part of its functional hazard assessment, it did not evaluate all the potential alerts and indications that could accompany a failure that also resulted in uncommanded MCAS operation. Therefore, “In the 737, the horn serves a dual purpose and thus is an ambiguous alarm. Before takeoff, it warns pilots if the aircraft is not configured properly for flight. Pilots have frequently misinterpreted the in-flight warning as an indication of a preflight danger that is no longer a concern and have thus considered it a false alarm.” neither Boeing’s system safety assessment nor its simulator tests evaluated how the combined effect of alerts and indications might impact pilots’ recognition of which procedure(s) to prioritize in responding to an unintended MCAS operation caused by an erroneous AOA input.”
In this case, the sonic environment of the cockpit-the mass of alerts and warning sounds, in addition to the more mundane airplane noises-confused the crew of the plane rather than assisted them in addressing the problem they were facing. To be clear, the sonic environment Boeing designed did not cause the crash; that seems primarily to be a product of Boeing’s negligent and inadequate design and testing of MCAS. But faced with a new and challenging situation, the Lion Air pilots were further confounded by a mass of alerts that did nothing to clarify the situation (which was presumably why Boeing added those alerts to begin with) and, in fact, had the opposite affect.
And this is not a new problem with Boeing airplanes. In 2009, it was reported that 737 pilots had, for years, been ignoring an alarm designed to alert them to a depressurized cockpit-even after a plane in Greece crashed as a result of pilots ignoring the alarm and becoming incapacitated in flight. Part of the reason for ignoring the alarm is down to its design:
A World of Noise
One of the keys to good acoustic design is knowing when not to add sound to a product. Unfortunately, restraint in this area is not common in technology and design industries, largely because there is so little knowledge of how sound shapes people’s multisensory responses and interactions with products. We live in a world where all our tech makes noise at us virtually all of the time. Some of it is sound that we specifically seek out, such as when we stream music on our phone; some of it is sound that helps us interact with the world, like audible crosswalk signals and subway announcements.
But a substantial part of the sound we experience has no particular necessity, whether for enjoyment or information. Much of the sound in our lives is simply noise, cluttering up our acoustic ecosystems and making it harder for us to distinguish the sounds that we actually do need in order to get around and stay safe. Sometimes this clutter is relatively benign, but as with the many airplane examples, sometimes it can have deadly consequences. And until industries take their sonic designs seriously-by researching their impact and making sound an equal partner in product design-it is difficult to envision an end to the tragic outcomes of sonic clutter.
Originally published at https://www.linkedin.com.
