Broken Glass Procedures
Understanding and Navigating Glass Avionics Failures
By William Dubois, guest writer
Instead of “break glass in case of emergency,” in the modern flight deck, “broken glass” is an emergency in and of itself — a first-rate emergency that can spiral out of control with mind-numbing speed. Sure, modern glass avionics are the gold standard for reliability — much more reliable, on average, than their analog pneumatic- and electric-gyro predecessors. That said, anything that humankind makes can break. And when reliability meets Mr. Murphy, the next steps for pilots flying glass are different from those flying steam.
To understand what those operational differences are, we first need to look under the cowl and understand the magic that drives the displays. While the system architecture of glass panel avionics varies by manufacturer and model, all share some basic DNA: the “glass” display itself, the pilot interface, and the black boxes that drive the system. Let’s start with the boxes.
Little Boxes
A glass panel system is controlled by two different black boxes, in concept (more on that in a moment). The first box is called an attitude and heading reference system, or AHRS in our acronym-laden lexicon. The AHRS is responsible for interpreting pitch, bank, and heading info. It does this using accelerometers, mini gyros, a magnetometer, and … well … magic. The second box is the air data computer, or ADC, and it’s responsible for altitude, airspeed, and vertical speed number crunching and display.
While the system architecture of glass panel avionics varies by manufacturer and model, all share some basic DNA: the “glass” display itself, the pilot-interface, and the black boxes that drive the system.
There may be one of each type of box in the aircraft, or, in some installations, there may be dual AHRS and/or dual ADCs. Increasingly, there are units in the field where the ADC and the AHRS systems are combined into a single box, called, you guessed it, an ADAHRS. And, in some systems, the boxes themselves are gone, with the hardware for both built right into the pilot display, an approach that greatly simplifies installation, and reduces weight, cost, and complexity.
All this variability, along with the rapid pace of technological advancement in contemporary avionics, means that you need to spend some time with the Pilots Operating Handbook (POH) and/or flight manual supplement for any glass panel-equipped aircraft you fly so that you know how the systems are laid out. Flying glass without this knowledge would be akin to jumping into a strange airplane without first understanding how its fuel system is designed. Not to mention, it’s your responsibility under 14 CFR section 91.103, Preflight action, to familiarize yourself with all available information regarding the flight, which includes the proper use of avionics installed in the aircraft.
Pilot Interface
The newest glass panel systems are driven by touch screens that feature smartphone-esque icons sporting highly intuitive menus. That said, the bulk of the glass systems found in the general aviation fleet are still button, knob, and softkey driven, often with less than intuitive menus and button press chains required to achieve the desired results. These analog-entry glass panel systems all feature inverse workload: once mastered, they are great workload reducers in the air; but to master them, expect significant ground study.
To avoid draining the aircraft’s battery, a ground power supply is recommended for in-airplane ground work. As an alternative, investigate the availability of flight simulators or training devices in your area that match up to the avionics in the aircraft you will be flying. Sims have several other advantages over sitting in the airplane pressing buttons and practicing flows, including the fact you can practice (safely) in simulated flight, as well as on the ground — and they are cost-effective compared to burning avgas or JetA.
Additionally, some glass avionics systems have “emulators,” or desktop computer programs that mimic the flight deck systems so that you can learn — and keep sharp with — the flows from the comfort of home.
Contrary to popular belief, a glass panel system isn’t totally high tech. The ADC still uses the aircraft’s ol’ fashioned pitot static system to connect to the flight environment.
Two Screens
The vast bulk of contemporary glass installations on light GA airplanes feature a pair of display panels, the pilot side panel being called the primary flight display, or PFD; and a second display of the same size on the copilot side called an MFD, for multi-function display. The PFD is generally used to display the flight instruments, while the MFD displays navigation and in some cases, engine data.
The beauty of two screens, beyond being beautiful to the eyes of many pilots, is the fact that the screens can often flip-flop data. So not only do the dual screens provide a greater ecosystem of situational awareness, but they also serve a redundancy role. If the PFD screen suffers a failure, the flight data can merely be shifted to the MFD or in some cases, a backup electronic display.
Of course, now everything you need to see and know to control flight is on the wrong side of the airplane. So here’s your first tip and challenge: on your next instrument proficiency check, shoot an approach using the MFD. Flop your data and dim, or cover, your PFD — as, generally speaking, most manufacturers discourage disabling the PFD by pulling its circuit breaker.
Bonus points for getting with a flight instructor to get some right-seat time. If you are flying alone and lose your PFD, that experience will make MFD flying more natural. That said, if you are not an instructor yourself, you might find the landing sight picture (and the opposite hand throttle/yoke operation) disconcerting at first, which is why some practice with an instructor is in order.
Of course, in a real-life display failure, you are now essentially flying on one mag. Sure, like magneto systems, the odds of losing both are pretty remote, but why take the chance? If you’ve lost one display, it’s time to get on the ground at the nearest airport.
In the case of an alternator failure in a glass flight deck, it’s critical to quickly shed load on the electrical system.
Reliability’s Weakness
Despite the greatly improved reliability of glass avionics compared to legacy avionics, if there is a failure in a glass system, their architecture makes them more prone to system-wide failures. That means you can lose all of the flight data, compared to analog systems failures, where you are more likely to only lose either the air-driven or power-driven instruments — leaving you with at least a 50% solution.
Hence, in glass flight decks, there is a need for standby instruments.
Standbys
Standby, or emergency backup instruments, might be a set of analog instruments, or they can be an independent miniature glass panel system. Either way, the standby system is your lifeboat in the “IFR sea.” Should the worst happen to your primary system in hard IFR, you can still aviate and navigate to an island of safety.
At least in theory.
Because the reality is that standbys are both small and inconveniently located, typically low down on the panel. Yes, you can fly on them. And yes, it will be a “stressfest.” So that’s your second tip and challenge for today: on your next IPC, shoot a hooded approach on your standbys.
It’s Not as Modern as You Think
Contrary to popular belief, a glass panel system isn’t totally high-tech. The ADC still uses the aircraft’s ol’ fashioned pitot static system to connect to the flight environment. That, in turn, means that contemporary glass panels can fall victim to the same pitot-static failures that legacy avionics do, so it pays to review the symptoms of pitot and static blockages. Also contrary to popular belief, the systems won’t necessarily alert you to a pitot-static problem, and, for the same reason, it can be hard for pilots to recognize such failures in analog systems — they are subtle and tricky to recognize.
Power Hungry
When it comes to being prepared for emergencies, the number one thing to understand about glass avionics actually has nothing to do with the glass itself directly, but rather with the glass’s food. Modern avionics have ferocious appetites for electricity. So much so, that an alternator failure is possibly a greater emergency than an avionics failure. This is because once the battery is drained — and the battery-backup, if so equipped — the glass shuts down along with the radios and all the rest.
An alternator failure in a glass-equipped flight deck is a much more serious matter than it is in a legacy flight deck. First off, once the battery is dead, all flight instrument data on the glass is lost — rather than just a portion of it. Additionally, the time from alternator failure to system failure is dramatically reduced, due to the power-intensive nature of glass avionics.
In the case of an alternator failure in a glass flight deck, it’s critical to quickly shed load on the electrical system. Unplug any personal devices that are suckling on the airplane’s USB ports. Then promptly follow the checklist to shut down any unnecessary aircraft power usage.
Speaking of unnecessary power use, in IFR conditions, consider proactively lightening the load on your electrical system. This means not taxing the aircraft’s electrical systems by using it as a charging port for crew and passenger tablets, phones, or laptops — their charging load can increase the risk of an electrical system failure.
Lastly, don’t expect the lights to stay on as long as the POH says they will after an alternator fails; that number is based on a factory-new battery. As batteries age, their stored load capacity decreases. In an alternator failure, the clock is ticking on your glass avionics. Actually, it’s not so much a clock, as a stopwatch. It is critical to get to VFR conditions, or safely on the ground as quickly as possible.
For maximum preparedness, take the time on the ground to study the architecture of the glass panel systems of any glass aircraft you fly.
The Right Stuff
In all flying, the key to emergency survival is preparedness. In the case of glass IFR flight, avionics failures are less likely, but when failures happen, they are more likely to be widespread. Additionally, know that glass avionics are more vulnerable to aircraft electrical system failures than legacy systems are, and be ready to act swiftly.
For maximum preparedness, take the time on the ground to study the architecture of the glass panel systems of any glass aircraft you fly. Practice flows — standard, atypical, and abnormal/emergency — parked on the ground, in a sim, or using an emulator. And review those tricky pitot-static failures, and how they would manifest on your glass display.
In the air, put those IPCs to good use by practicing with the MFD and the standbys. Consider some right-seat time. Right-screen, right-seat practice equips you with the right stuff for a glass emergency.
In flight, keep the load light — the power load. Just like weight affects aircraft performance, so too does the load on the electrical system.
And should it happen — should the infamous red “Xs” appear, or a screen go dark — unplug and navigate to the nearest port in the storm, be that below the weather, above the weather, or on the ground at the nearest airport or airstrip. Time is not on your side. But if you are prepared, there will be time enough.
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William E. Dubois is a widely published aviation writer and the ground school program manager for Infinity Flight Group. He holds a commercial pilot certificate with an instrument rating and is a dual-accredited master ground instructor.
