Bells, Chimes, and Clicks, Oh My!

Today's state-of-the-art aircraft interior technology for suppressing noise in business jet cabins combines with advanced electronics in flight decks to create the highest level of safety and comfort for both passengers and crew. However, one of the unintended consequences of quieter cabins is that passengers often hear sounds emanating from the cockpit that are unfamiliar and may feel alarming.  

Even with the cabin/cockpit door closed, the muffled sounds of bells, buzzers, chimes, horns, clicks, and even some computerized word phrases can filter into the cabin, and with good reason. These noises are loud enough to overcome other less vital cockpit sounds in order get the attention of the pilots who are sitting in the noisier nose section of the aircraft—and usually wearing headsets or earbuds to communicate with each other and air traffic controllers. The sounds are designed to alert the crew to potential safety hazards and ensure proper handling of the aircraft. 

So, what are the sources for some of these sounds?  First, it's likely that a cacophony of different sounds and words will be overheard by passengers even before takeoff. Part of the preflight requirements for the crew are to test routine and cautionary aural alerts and warning alarms to ensure that they are functioning correctly. These tests include engine fire alerts (a short burst of bells), ground proximity warning systems ("terrain" or "woop, woop, pull up"), and aural overspeed warning devices (a clacking noise). 

Once airborne, passengers may detect more routine and repetitive sounds that occur throughout the cruise portion of a trip. For example, a clicking that mimics a cricket chirping can continue for a moment, several seconds, or longer. The source of the clicking is a device known as the "trim wheel" that continuously moves when small aerodynamic adjustments are made to ensure the aircraft maintains a level and smooth flight. Each time the wheel moves, either manually by the pilot or automatically by the autopilot (AP), it makes a click to let the crew know that the trim input is functioning. In some aircraft, the crew can switch off this aural trim feature and other routine non-emergency aural alerts. 

Speaking of the autopilot (AP), passengers may hear chimes when the AP is disengaged. These sounds alert the crew in case the AP disconnects inadvertently. A different chime or short ring alerts pilots when the aircraft is leaving a current altitude or nearing a newly set altitude. As the aircraft nears that pre-set figure, passengers might hear the word "altitude," alerting the crew that they need to level the aircraft. Passengers can expect to hear "altitude" more frequently when the aircraft is climbing on departure or descending on approach. 

On the final approach to landing, passengers may hear a distinctive "beep" sound that quickly rises and fades. This momentary sound is informing the pilots that they have passed over a signal called the "outermarker," an electronic navigation fix that is one of several indicators in the cockpit that verifies that the crew has the aircraft on the correct final approach path. Passengers can expect to hear this alert as well as other sounds associated with landing in inclement weather. 

Helicopters Sound Different

In the more confined space of small and mid-size helicopters, where there is no door separating the cabin from the cockpit, passengers rarely hear aural alerts and warnings because engine noise is more prevalent than in fixed-wing aircraft—and passengers are usually wearing sound-reducing headsets to communicate with each other and the pilots. However, unlike aircraft with cabin/cockpit doors, helicopter passengers facing forward have an unobstructed view of the instrument panel to wonder what all those gauges and colored bars mean. Stay tuned for a future article!