Glass cockpits and avionics

Read the data source behind the display

A primary flight display (PFD) gathers attitude, airspeed, altitude, vertical speed, heading and navigation information into one presentation. A multifunction display (MFD) commonly provides maps, engine information and other selected pages. What each screen can display, and whether it can substitute for the other, depends on the installation.

An attitude and heading reference system (AHRS) uses inertial sensors and processing to provide attitude and heading. A magnetometer supplies magnetic-field information in many systems; some designs use additional aiding data. An air data computer (ADC) processes pitot, static and temperature inputs to produce air-data values. GPS position is another input, not a substitute for all attitude and pressure sensing.

Separate the layers: sensor measures, computer processes, data path carries, screen displays, electrical source powers. Loss of a screen is different from loss of the sensor feeding it. Moving information to a working screen can help after a display failure, but cannot repair a failed common AHRS or ADC.

IFH 5-22–5-23: AHRS and ADC · IFH 11-4: electronic display malfunction

A backup needs a source, a supply and a procedure

Identify the alternator/generator, main battery, buses, circuit protection and any standby battery for the actual aircraft. Know what the electrical-status indications mean: a loadmeter and a battery charge/discharge ammeter do not measure the same thing. A failed charging source can leave displays operating on the battery while available electrical time is decreasing.

Trace what survives each failure. Does the standby indicator have its own attitude sensors? Does it share the static system? Does its battery require a preflight check or particular switch position? Which radios, navigator, lights, pitot heat or trim remain powered by the available bus? Never infer an endurance, bus assignment or switch sequence from another airplane.

Some installations provide reversionary or composite display modes that transfer selected flight and engine information to another screen. Learn exactly how that mode is selected, what data it uses, and what information disappears. It is a display arrangement, not a promise of independent sensors. Other installations have different backup methods.

A screen with a moving horizon is not automatically healthy. Include source flags, data-validity annunciations and electrical status in the cross-check. The failure-recognition lesson develops the evidence; actual switching and load-management actions come from the aircraft checklists.

IFH 11-4–11-7: display and electrical failures · PHAK Chapter 8: electronic instruments and power-source awareness

The active leg and selected source govern guidance

An installed RNAV/GPS navigator or flight management system (FMS) stores and manages a route and supplies navigation guidance. GPS describes a positioning system; WAAS augments suitable equipment with additional accuracy and integrity information. Available approach functions depend on the approved installation, current service conditions, and its annunciations.

The moving map, active flight-plan leg, selected CDI/HSI source, and autopilot mode must describe the same intended operation. A magenta route drawn on a map does not prove that the CDI is using GPS or that the autopilot is following it. A system may instead be using heading, VOR/localizer, another navigator, or a different leg.

When entering a clearance, verify fixes in order, the active leg, any discontinuities, the intended lateral and vertical procedure, and the source/mode annunciations. Cross-check the proposed change before executing it, then check the resulting path. A database contains available procedures, not an ATC clearance to fly them. Do not let lengthy programming replace the aircraft cross-check.

The navigation lessons will teach VOR, CDI/HSI and GPS/RNAV use in detail. Here the goal is to explain how selected source, route and mode affect what the avionics are commanding, and to recognize when they no longer support the planned operation.

IFH 5-26–5-27: flight management systems · AIM 1-1-17 and 1-1-18: GPS and WAAS operation and limitations

Command guidance and control engagement are different

A flight director (FD) computes steering commands and displays command bars or cues for selected modes. The attitude presentation shows the aircraft's measured attitude; the command cue shows the attitude the system is asking for. The pilot can hand-fly those commands. Visible FD bars do not prove that the autopilot is engaged.

An automatic flight control system (AFCS) can include the autopilot, flight director, trim and other functions. The autopilot moves controls through servos to follow its active modes. The installed system may control roll, pitch or other functions in a particular combination. An altitude preselector is a selected target, not proof that altitude capture is armed or active.

The AFCS depends on particular attitude, rate, air-data and navigation sources. A failure can remove a mode, produce misleading commands, or require disengagement. Confirm its actual limitations and procedures: engagement/disengagement conditions, minimum use heights, speed range, approved approach coupling, trim behavior, turbulence/icing restrictions and required checks. This lesson supplies no universal limits.

Know the published normal disconnect and malfunction actions before use. If automation commands an unintended path or uses suspect data, maintain control and apply the appropriate AFCS procedure. Disconnecting the autopilot may not remove FD commands in every installation; verify the remaining annunciations and use the aircraft's guidance. Never assume that continuing to follow a cue solves a source failure.

IFH 5-23–5-26: flight director and autopilot systems · ACS II.A: AFCS knowledge, risk and aircraft-specific familiarization

Read what is active, what is armed and what happened

Active means the mode currently supplies guidance or control. Armed means it is waiting for specified capture or activation conditions. Pressing a button is a request; the annunciation and aircraft response confirm the result. Colors, labels, capture logic and default modes vary, so learn the installed presentation.

Before a change, state the intended path and mode. After selection, read the annunciation, check attitude/performance and monitor the transition. This sequence prevents mode confusion: believing the system is doing something different from what it actually controls.

Automation does not automatically supply speed protection or manage engine power. For example, if a system holds a selected climb rate without controlling thrust or protecting airspeed, declining climb capability can make airspeed decay. Monitor airspeed, power and vertical performance, and adjust the plan under the aircraft procedures rather than protecting the selected rate at all costs.

Common error: spending attention on the flight-plan page while a new vertical mode quietly changes the flightpath. Reduce programming workload, use a simpler appropriate mode or hand-fly as trained, and request time or an amended clearance when needed. Automation is useful only while the pilot understands and verifies its behavior.

IFH 5-23–5-26: mode selection, FD and AFCS · IFH 6-24, Section II: electronic display cross-check and common errors

Surveillance and advisory displays have different jobs

A transponder provides surveillance replies, including assigned code and, with applicable equipment and mode, pressure-altitude information. Mode S has additional identification/data functions. ADS-B Out broadcasts aircraft information using an approved position source; ADS-B In receives information for compatible cockpit displays. A portable ADS-B In receiver does not itself provide required ADS-B Out.

Verify the actual transponder controls, altitude-reporting status, identification and ADS-B installation. Its pressure-altitude reporting reference differs from the pilot's local altimeter setting; changing that setting does not directly change encoded pressure altitude. Report a surveillance malfunction to ATC and follow applicable guidance rather than assuming a traffic picture proves successful transmission.

Advisory traffic can omit targets and depends on equipment and coverage. It helps acquire traffic; it does not provide an ATC clearance or authorize avoidance maneuvers solely from a TIS-B target. Datalink weather also has collection, processing and transmission delay. Use it for strategic awareness, not close thunderstorm penetration or tactical weaving between cells. Check product times and coverage.

AIM 4-5-7, 4-5-8 and 4-5-9: ADS-B, TIS-B and FIS-B · AIM 4-1-20: transponder and ADS-B operations · IFH 5-7: encoding altimetry

Prepare the EFB as a fallible information tool

An electronic flight bag (EFB) can hold charts, checklists and planning information. Under the current AC 91-78A guidance for Part 91, electronic information can replace appropriate paper references when the guidance is met; an EFB does not thereby replace required navigation, communication or surveillance equipment. The AC is advisory, not a regulation.

Before flight, verify current and valid information, download the needed material for offline use, check power, secure the device and choose readable lighting. Cross-check entries and computed results. Plan another usable way to obtain the needed information if the device or application fails. Heat, depleted batteries, connectivity, glare, storage and handling can interrupt access.

Practice finding a chart and checklist without head-down searching. Discuss distraction, device placement and interference. A tablet own-ship symbol or synthetic-view feature is not automatically an approved flight-navigation or attitude source. Check the authorization and limitations of the actual equipment rather than relying on appearance.

AC 91-78A, §§9 and 11: reference replacement, assessment and training

Rehearse the actual installation with an instructor

For ground preparation, use the applicable AFM/POH and approved avionics/AFCS supplements to build a source and power map. Point to source-status annunciations, the navigation-source selector, active/armed mode indications, normal disconnect controls, and the published backup/reversion method. Explain which capabilities remain after a screen, sensor or charging-source failure.

In an approved ground trainer or an instructor-directed cockpit session, rehearse a route change and verify the active leg, CDI source, modes and resulting guidance. Explain the limits of the installed GPS/WAAS, flight director and autopilot. Rehearse EFB preflight, offline chart retrieval, input checks and loss-of-access alternatives. Use published checks and simulator methods; do not pull breakers or disable aircraft equipment as a casual exercise.

These are preparation activities for ACS II.A.S2, II.B.S1 and II.B.S2. Lesson completion records study only. It does not demonstrate operating skill, AFCS proficiency or the flight performance required on a practical test. Equipment familiarization and instructor-led operation in the actual installation are still necessary.

Unfamiliar avionics and an excessive level of automation add risk in cloud. Be ready to simplify the task and maintain a usable instrument cross-check. A clearance, available autopilot and current pilot certificate cannot substitute for knowing the particular aircraft.

ACS II.A.S2, II.B.S1/S2; I.A.R4 and IV.A.R3 · AC 91-78A §11: assessment and training · IFH 5-23–5-26: system-specific FD and AFCS operation

FLIGHT SCENARIO

What would change your plan?