There’s no worse feeling in aviation than finding yourself with a serious risk to the safety of your flight. It hits you in the gut and sets the adrenaline pumping. It brings you to focus faster than a Formula 1 green light. It’s times like this that you need to put on your calm and collected hat. You need to assess the situation and make your decisions according to highest priority. First needs first.
But you can’t make decisions if you don’t have all the information. And when the situation includes conflict with another aircraft or conflict with terrain, the situation is even more dynamic. You need real-time assistance and support. This is where your friendly neighborhood air traffic controller comes in handy.
*ATC has Entered the Chat*
Our primary concern as air traffic controllers is to prevent a collision in the National Airspace System. Whether between two aircraft or between aircraft and terrain, all other priorities take a back seat to this prerogative. Second in command of our hierarchy of priorities, is providing Safety Alerts. Safety Alerts are one of, if not the, most important service that ATC provides.
What’s a Safety Alert?
Safety alerts are urgent advisories issued for both IFR and VFR to avert potential collisions or hazardous situations. These alerts are a critical service to pilots and act as a proactive measure to prevent an imminent conflict between aircraft and terrain/obstacles or other aircraft. As outlined in the FAA Order 7110.65 (the holy grail of regulations for ATC), air traffic controllers are tasked to “Issue a safety alert to an aircraft if (they are) aware the aircraft is in a position/altitude that, in (their) judgment, places it in unsafe proximity to terrain, obstructions, or other aircraft.”
Controllers will issue the safety alert to the aircraft, and continue issuing it, until the pilot informs the controller that action is being taken to fix the situation at hand. As a side note, controllers are even instructed to be vigilant of situations that aren’t within their area of responsibility. If they observe a situation that requires a safety alert, they are expected to notify the responsible controller immediately.
There are two primary types of safety alerts that controllers will issue: Terrain/Obstruction Alerts and Aircraft Conflict/Mode C Intruder Alerts.
Each safety alert has its own specific phraseology that ATC is required to use when issuing the alert. As I expect you know by now, proper phraseology is a critical component of any transmission. It ensures effective communication between ATC and pilots. One of the primary traits of effective communication is a common “language” that both participants understand and speak fluently.
Phraseology for safety alerts has changed over the years, evolving with the goal of being clearer and more concise, but this is what you can expect right now:
Terrain/Obstruction Alerts
LOW ALTITUDE ALERT (call sign), CHECK YOUR ALTITUDE IMMEDIATELY.
If the aircraft is not yet on final approach, THE (as appropriate) MEA/MVA/MOCA/MIA IN YOUR AREA IS (altitude).
Example: “Low altitude alert, Piper One Three Delta Zulu, check your altitude immediately.” Or “Low altitude alert, Piper One Three Delta Zulu, check your altitude immediately. The MIA in your area is one six thousand.”
Aircraft Conflict/Mode C Intruder Alerts
TRAFFIC ALERT (call sign) (position of [traffic]) ADVISE YOU TURN LEFT/RIGHT (heading), and/or CLIMB/DESCEND (specific altitude if appropriate) IMMEDIATELY.
Example: “Traffic Alert, Cessna Three Four Juliett, 12’o clock, 1 mile advise you turn left heading 270 immediately.” Or “Traffic Alert, Cessna Three-Four Juliett, 12’o clock, 1 mile advise you turn left and climb immediately.”
The generally accepted best practice for controllers issuing an aircraft conflict safety alert is to avoid specific headings or altitudes. This reduces the time needed because the pilot needn’t consider a specific heading or altitude. Pilots should react to the imminent nature of the alert. A safety alert is not issued lightly by ATC, so an appropriately urgent action should be taken.
You are Responsible
As pilot in command of your aircraft, you are solely responsible for the action you take to resolve the safety issue. You are closest to the situation and will have the most accurate information available. Air traffic control is constrained by equipment and information limitations.
Radar has lag time and accuracy deviation, especially for centers. This is due to the large areas they cover. This explains why the lateral separation required by en-route ATC is five miles. It’s precisely due to the time lag and accuracy deviation inherent in their radar systems. It’s the same for terminal radar (radar service within ~30 miles from the airport). However, because their radar is faster and closer to targets, the separation requirement is three miles. But still…MILES! If radar was precise, ATC would merely need to keep radar targets from merging.
This is why in the aircraft conflict/mode C intruder alerts, the phraseology is “Advise you turn left immediately” or “Advise you descend immediately.”
Now, with the implementation of ADSB technologies, current information is more reliable and accurate than in the past, but the assurances and accuracy of separation with ADSB are not tested/confirmed, so the required separation and available ATC services have not been changed.
In other words, ATC is far removed, but you are right there—you have the responsibility to take appropriate action.
A Couple of Examples
The first example is of a terrain/obstruction safety alert that (should have) occurred in mountainous terrain with a GA aircraft on an IFR flight plan. We’ll call them N13DZ. N13DZ was flying through an area of IMC where they began to pick up moderate icing. The pilot called ATC with the report and requested a lower altitude in an attempt to exit the icing. Unfortunately for them, they were at the Minimum Safe Altitude (MIA). ATC was unable to give them clearance to a lower altitude.
N13DZ was reluctant (or perhaps it was unable) to climb. They continued for a number of miles with no luck in exiting of the icing. They relayed this information and their concern to ATC. The controller made the decision to declare an emergency on the pilot’s behalf, with the intention to descend the aircraft beneath the MIA. The controller reasoned that because MIAs in mountainous terrain are based on a separation standard of 2000 feet from the highest terrain/obstacle, it would be reasonably safe to issue the decent. N13DZ descended below the MIA, exiting the icing, but encountered another unsafe situation…
It needs to be said that according to the 7110.65, controllers may take actions that they deem to be reasonably safe during emergency situations. The regulation (7110.65, 10-1-1.d.) tells air traffic controllers this:
“Because of the infinite variety of possible emergency situations, specific procedures cannot be prescribed. However, when you believe an emergency exists or is imminent, select and pursue a course of action which appears to be most appropriate under the circumstances and which most nearly conforms to the instructions in this manual.”
Now, what is the “most appropriate” action under this circumstance?
The controller determined that issuing a descent beneath the MIA was the most appropriate action to accommodate the pilot’s effort to exit the icing. The clearance beneath the MIA did in fact allow the pilot to exit the icing condition, but they encountered another issue shortly after.
N13DZ continued at that altitude for a few miles before receiving a terrain alert from their Ground Proximity Warning System (GPWS). Their trajectory and altitude was below upcoming terrain. The pilot climbed to a safe altitude and continued until exiting the IMC and eventually received clearance from ATC to an altitude above the MIA.
Legally speaking, if an accident were to occur (it did not), it is arguable to say that issuing a clearance beneath the MIA was not the most appropriate action to take. A more appropriate course of action might have been to issue a terrain/obstacle safety alert and provide the pilot with all the information available to the controller, i.e. the MIA in the area, the fact it is mountainous terrain (nearest obstacle/terrain is 2000 feet below the MIA), etc.
Key takeaway: When encountering situations involving terrain/obstacles, you should rely on your own judgement for action. ATC normally won’t (or shouldn’t) issue clearances when you are below minimum safe altitudes because they can’t ensure separation. ATC is a resource of information in these situations. Consider asking where to find a nearby area with lower safe altitude minimums. Carefully evaluate your surroundings and the appropriate actions to take.
This Time, Traffic
This next situation is a good example of both an aircraft conflict alert and a readback/hearback mistake.
The scenario starts with an eastbound departure out of KLAS, SWA1023, entering a new sector vertically while climbing out of the sector below. SWA1023 checked onto the new frequency climbing out of FL200 to FL250. The air traffic controller acknowledged the pilot’s check-on and issued a climb to FL270, 1000 feet below opposite direction traffic at FL280, and told the pilot to expect FL330. SWA1023 read the clearance back almost verbatim, with one very nasty mistaken difference.
SWA1023: “LA Center, SWA1023. FL200 climbing FL250.”
LA Center: “SWA1023, LA Center. Climb and maintain FL270. Expect FL330 after traffic.”
SWA1023: “Roger, climb FL270. Expedite FL330 for traffic, SWA1023.”
As you likely guessed, SWA1023 blasted through FL270 in their expedited climb to FL330.
ATC has many tools that assist in traffic situations like this. Chief among those alerts is a visual alert that causes the two data blocks associated with the aircraft on the radar screen to “flash” or blink brightly. This conflict alert occurred, and the controller immediately took steps to separate the traffic.
The controller issued the traffic alert: “SWA1023, traffic twelve o’clock, three miles, FL280. Descend and maintain FL270 immediately.”
The pilot, responding to the severity in the controller’s clearance, descended as quickly as possible (needing time to stop the climb and start the descent) and leveled off at FL270.
In the review of the event, both aircraft were measured to have come within 300 feet vertically and a quarter mile laterally of each other. It was also discovered that, because of the discrepancy between radar lag and climb rate, SWA1023 was already above the traffic when the controller issued the safety alert and clearance back down to FL270. Following the instructions of the controller, SWA1023 descended back through the flight path of the traffic.
Did the controller make an error in judgement by descending SWA1023 back to the originally assigned altitude?
I think it is difficult to find the controller at fault for this, due to the radar lag and not knowing the SWA was in an expedited climb. However, what is something the controller did do wrong?
The controller did not say, “advise you descend and maintain FL270 immediately.”
An aircraft conflict/Mode c intruder alert is always followed with a suggested action, not an actual clearance. The pilot is always in the best position to make the quick decision necessary to maintain safety in those situations. Is the suggestion of ATC the best course of action in most cases? Probably. But it is never the required action during aircraft conflict/Mode C intruder-alert situations.
So if you find yourself in situations like these, remember your responsibility and that of ATC. Consider your options and take the appropriate action. And always remember that ATC is there to help and will do everything they can to keep you safe.
Mac Lawler has 13 years of experience in air traffic control. He specializes in training and development and is motivated by continuous learning. His favorite airport is most definitely not Atlanta. He carries a storyteller’s license and abuses the privileges it affords him, especially when talking about Atlanta.
