Since the earliest days of aviation, pilots have been staring at gauges to help ascertain the condition of their machines and the world around them. Orville and Wilbur had three instruments on their first Flyer: a stopwatch, an anemometer for measuring wind speed and a tachometer. Subsequently and especially since the introduction of instrument flight and the development of the standard T cluster, engineers managed to cover every available inch of cockpit real estate with some type of instrument, button or switch.

As aircraft became more complex, large passenger and military aircraft required a flight engineer to manage the systems and scan the dozens of gauges and lights, thereby freeing the pilots to concentrate on aviating. In the late 1960s and early 1970s, the military sought to de-clutter its cockpits by using small cathode ray tubes (CRT) to replace the mechanical gauges and combine the functions of several instruments onto a computer-generated screen. This was the genesis of the glass cockpit - centering initially on the Primary Flight Display (PFD).

From an aircraft systems perspective, the cockpit's traditional round "steam" gauges provide the flight crew with constant status information. It is up to the pilots to scan the gauges, looking for misbehaving temperatures and pressures. However, unless an advisory threshold is reached, causing the Master caution to illuminate, dangerous trends could go unnoticed until too late. A NASA study completed in the 1970s determined that pilots could be just as safe with a cockpit that provides system status on demand, instead of having information presented continuously via dials or tapes, and with the introduction of "glass," designers embraced that concept. Soon, the rows of steam gauges and banks of caution lights gave way to the Multi-Function Display (MFD). This new display was kind of a general store of aviation data, providing a home for the weather radar, flight planning, GPS navigation aids, enhanced ground proximity warning, TCAS II and even control of the comm/nav radios.

From a maintainer's perspective, the all-glass cockpit is an advance, and not. In many ways, the old electromechanical gauges were easy to maintain. If the thing was inoperative, you replaced it. They were relatively inexpensive and many were TSOed items, which made replacements easy to find. About the worst things that could go wrong were discovering the replacement had a short wire bundle and wouldn't reach the connector behind the instrument panel, or you had to apply tiny pieces of tape to the instrument's face for advisory ranges.

By contrast, an all-glass panel provides a seemingly infinite range of malfunctions: entire screens going dark in flight; mode switching that has a mind of its own; black lines; error codes and good old fashioned inoperable - all accompanied by troubleshooting nightmares. Obtaining replacement displays, which alone cost tens of thousands of dollars, plus the additional electronics like symbol generators, and processors can easily deplete your maintenance reserve budget. Keeping such systems operational and safe can be a resource and management headache.

Most pilots have embraced the all-glass cockpit and find the improved situational awareness tools and functionality beneficial to safe flying. With some flight departments postponing new aircraft purchases, now may be a good time to upgrade the cockpit to take advantage of the latest safety technology. This task usually falls on the maintenance manager's shoulders and there are many options from which to choose. How do you make good choices and end up with the best possible system? We asked fellow maintenance managers and upgrade experts to shine a light on what goes on behind the glass.

Though we tend to think that the cockpit displays are just fancy television screens, they are much more complex than your average flat-panel TV. The CRTs of old have been largely replaced by liquid crystal displays (LCD), which use much less energy and have much longer service lives. Early LCDs had poor glare characteristics and limited viewing angles, but advances in the technology now make the LCD crystal clear. The brains of the system are in the control/display computer that takes all of the sensor, condition and flight information and converts that digitally through the symbol generator, then passes the info to the display through the data bus.

The pilot's PFD contains flight and navigation information. Some systems allow pilots to customize this screen to a certain extent, but they cannot remove the basic information necessary for flight. Screens have grown in size from the early five-by-five-inch displays to 10 by 13 inches, and these can hold a lot of information. In an advisory mode, a de-clutter function will highlight whatever is the immediate problem and revert to a cleaner display. Several systems feature a cursor controller, which takes the form of a handgrip, trackball or joystick and is used by the pilots to point or scroll and adjust pages on the screens.

The newest, large-format MFDs go beyond providing flight environment and nav data and also replace the dials and caution panels to display aircraft mechanical and system operational data. Different OEMs have varying names for these additional functions: Engine Indication and Crew Alerting System (EICAS), Electronic Centralized Aircraft Monitoring (ECAM) and others. Aircraft OEMs have different ideas on how the PFD and MFD are positioned in the cockpit. Many aircraft are equipped with an additional MFD in the center position to further enhance the available information.

New technology brings new and complex challenges. Computers perform complex power checks and validation of sensor inputs and data crosschecks. If the inputs are out of tolerance, you will get an error code. Some codes are cleared by rebooting or recycling power, but persistent codes often indicate trouble. Fortunately for technicians, a properly designed system will have a logical troubleshooting manual that takes you through a set of steps to verify system health.