Post Pic

The Dangers of Assuming in ATC

How many times have you made an assumption based on the norm only to find yourself with egg on your face? Here’s a situation that presented itself on my watch sometime ago. Without the benefit of a previously coordinated flightplan, a scheduled flight which I shall refer to as XXX123 popped-up on the frequency  inbound […]




How many times have you made an assumption based on the norm only to find yourself with egg on your face?

Here’s a situation that presented itself on my watch sometime ago. Without the benefit of a previously coordinated flightplan, a scheduled flight which I shall refer to as XXX123 popped-up on the frequency  inbound to my airport for landing. The usual aerodrome information was passed along with the instruction to report 10DME from the airport where joining instructions were to be issued. Being a scheduled operation, I associated this flight with a particular aircraft type that is normally used on this route. With this assumption, I calculated the ETA and mentally assigned the order for landing. The sequence of events which followed obviously departed from my expectations, with no safety being jeopardized I might add. The order for landing however, had to be amended.

As it turned out, the type of aircraft used for flight XXX123 on that day was different, and flies at half the speed of the aircraft normally used on that route. Several failures occurred here; the non-receipt of a filed flightplan, and my failure to verify the aircraft type are just two of them. The purpose of this article is however, is not to look at the failures, but warn against making assumptions and perhaps offer an explanation for this human behavior.

I am pretty sure that air traffic controllers can relate to some situation in the past where an assumption was made based on norms, but have had a rude awakening when the situation plays itself out differently. I can readily recall another situation on another day where a colleague initiated an ALERFA following a bout of assumption that an aircraft was destined for that airport where he was on watch. These are clear cases of human factors at work. You see, humans are wired to perform tasks based on a history repetition, so we naturally repeat ourselves unless some other event occurs to steer us in a different direction.

The lesson here is to make every effort to determine the status quo, rather than to make any assumptions. This ironically is one of the pillars of ATC, “NEVER ASSUME, DETERMINE”.


One Response

09.01.09

I just had that discussion with my trainee the other day at the MILLE sector. We had an aircraft eastbound to New York Center nonradar airspace. The pilot request “20 offset, when able direct GRATX.” My trainee heard it [and] never bothered to determine whether the pilot referred to a 20 mile or 20 degree offset. My trainee assumed a 20 MILE offset which was fine. The pilot turn 20 DEGREES and immediately became a conflict for another aircraft. Assumption is the mother of all F-ups, ESPECIALLY in ATC. Good point to bring up.

Subscribe to my Blog

About Wayne Farley

Wayne Farley

I am Wayne, an aviation safety evangelist who once made my living working in the control tower. Engage me while I share my thoughts, experience, and news from the aviation world. After writing "13 Characteristics of an air traffic controller" in 2010, it went viral and established me as an unofficial ambassador for ATC.

.

Stalk me here:

Facebook Twitter LinkedIn Google+ RSS Feed


Dig Through My Archives

Follow on Twitter

Latest Tweets