In Part 1, we discussed flight crews’ misconceptions regarding threatening weather. Now, we’ll look at ATC’s perspective.
The avoidance of severe weather involves a collaborative working relationship between ATC controllers and pilots. Asking for a weather deviation seems “simple” from our perspective in the cockpit. However, air traffic controllers are looking at “the big picture,” considering how your deviation might affect traffic not only in their sector but also in adjacent sectors. Non-standard traffic flow due to diversion requests is not easy to anticipate because of rapidly changing weather, varying aircraft capabilities and new potential conflict points of converging traffic. There is a reduction in available airspace due to threatening weather, leaving less airspace volume for conflict resolution.
This requires increased manual (telephone) coordination with the controllers of the adjacent sectors. Narratives from the ASRS express the high workloads induced by “extremely time-consuming rerouting,” especially when it involves coordinating with a different ATC facility.
Radio frequencies become even more congested as aircraft ask to divert. This requires more radio occupancy time with avoidance actions and revised onward routing clearances, which is particularly problematic in busy traffic management areas.
There is a terse exchange between a New York JFK controller and the crew of an Aer Lingus flight that highlights this inevitable conflict (https://www.youtube.com/watch?v=w1r3XZQc4Zo). According to the JFK controller’s point of view, many aircraft had taken off along that same flight path without asking for any deviations. In contrast, the Aer Lingus flight crew refused to take a vector due to their judgment that the new routing would expose the aircraft to severe weather. The replay of the radar tape shows a small region of yellow returns that may not look threatening, but from the view of the Aer Lingus crew it was unacceptable. With threatening weather in other quadrants around the New York Metroplex, one can quickly guess the workload for the New York controllers as well as other flight crews. Evidently, many persons have watched this video for the entertainment value of a New York controller having a testy exchange with an Irish flight crew, but putting the entertainment aspect aside, it aptly demonstrates the threatening combination of traffic congestion and rapidly evolving convective activity. Convective activity is extremely dynamic, and it is impossible for controllers to predict exactly how aircraft will deviate.
ASRS reports clearly show the consequences when flight crews waited too long to deviate, which resulted in the aircraft flying perilously close to threatening weather (or worse…in the middle of it!), trying to make decisions with a radar picture that was badly attenuated, and making high-stressed requests to deviate. Conditions such as these sometimes led to the flight crew exercising their command authority to deviate from the ATC clearance to avoid severe weather when they were unable to get quick authorization for a weather deviation.
A Multitude of Failures
Hail encounters often produced a cacophony of failure messages. For example, an Embraer EMB-175 captain reported a number of system failures annunciated on EICAS following a hail encounter while departing Monterey International Airport (MMMY) in Mexico. Just before exiting IMC, the EICAS screen illuminated with these failure messages: AP FAIL, AT FAIL, ELEVATOR FAULT, RUDDER FAULT, YD FAULT. This high task load situation puts a premium on good CRM skills. In this incident, the captain took manual control of the aircraft. Due to the proximity of higher terrain, it was necessary to continue the climb. This established two of the most important tasks in an emergency: (1) Always make certain that the aircraft is kept under control. (2) Point the aircraft in a safe piece of the sky (away from threatening weather and terrain) where the flight crew can then begin to remedy the mechanical malfunctions. When a series of warning lights appear on an EICAS, the flight crew must prioritize which deficiency to address first. In this case, the crew decided to tackle the AP FAIL procedure with the use of the QRH. Even after completing all of the QRH procedures, the flight crew was left with the EICAS displaying AT FAIL, STALL PROT FAIL, AOA LIMIT FAIL and WINDSHEAR FAIL.
Flight crews often reported that the outer panes of the windshield took a beating and were structurally compromised due to the cracks. Speed, altitude and cabin pressurization reductions are common specified procedures in aircraft flight manuals for a compromised windshield. For example, the Beech B200’s abnormal procedures section for a cracked or shattered windshield prescribes maintaining an altitude of 25,000 ft. or less, resetting the pressurization controller to maintain a cabin differential pressure of 2.0 to 4.6 psid, and then depressurizing the cabin prior to touchdown.
The aftermath of a hail encounter can quickly induce high cognitive workloads because of the necessity to descend to lower flight levels to reduce the stress on the cracked windshield, and perhaps needing to dump fuel to get down to landing weight if an immediate landing is warranted. ASRS reports indicated situations in which trying to obtain the necessary information to divert to a safe airport as well as computing the fuel needed for the divert at a lower altitude and slower airspeed resulted in excessive flight crew workload and sometimes resulted in a low fuel situation.
It is also worth noting that air-carrier flight crews often expressed a lack of confidence in the “flight following” of their dispatchers. “Contributing factors to this account are the apathy and lack of initiative from our company dispatcher. His initial briefing was completely inadequate. The thunderstorms blossomed during our time en route, and the dispatcher made no attempt to call us.”
Summary
These ASRS reports illustrate that exasperated flight crews do not have the information presented in a manner to suit their exact needs and criticality, especially in the dynamic environment of rapidly growing convective activity. Pilots need accurate, timely and appropriate information. They especially need precise information regarding the occurrence, position and intensity of the severe weather that produces the localized short-lived hail shafts. Early collaboration with ATC on a re-route is more likely to result in lower workloads for all, lower radio congestion and keeping one’s aircraft farther away from threatening weather.
Related Content
