Flight Management, Navigation Flashcards
Is IRS output information independent of or reliant upon external navigation aids?
Independent
Uses 3 sets of laser gyros and accelerometers to compute all IR data
-attitude
-true/magnetic heading
-acceleration
-vertical speed
-ground speed
-track
-PPOS
-wind data
How long does IRS alignment take?
Full alignment on the ground OFF to ALIGN/NAV, or loses power
-5-17 min
-req AC or DC power
-if positioned OFF in flight, full NAV can’t be restored till on ground
-PPOS initialization through FMC (normally) or through ISDU keyboard. Aircraft Must be stationary
Fast alignment (not normal, unless “strong gusty conditions” and normal alignment doesn’t work)
-30 sec
When does the ALIGN (white) illuminate steady on the IRS panel?
Illuminates steady when respective IRS is operating in either the:
-ALIGN mode
-initial ATT mode, or
-shutdown cycle
What does a flashing ALIGN (white) on the IRS panel during preflight indicate?
Fault (moved during alignment)
No position
Bad position
Alignment cannot be completed due to
-significant difference between previous and entered positions
-present position entry unreasonable
-no present position
Without AC power, how long can the IRSs operate? What light(s) will you see?
Backup DC power to the right IRS is automatically terminated if AC power is not restored within 5 minutes
*If AC power is not normal/removed, either/both systems auto switch to backup DC power from Switched Hot Battery Bus and ON DC caution light illuminates
What does a VERIFY POSITION FMC scratchpad message indicate?
The latitude/longitude position is not within 4 nm of origin airport
If the entered lat/long position doesn’t pass the IRS internal comparison test, the scratchpad message ENTER IRS POSITION is displayed
How many GPS receivers are installed?
2 independent receivers installed
GPS operation is automatic
Each GPS provides data to its associated Multi-Mode receiver (1 or 2). ADIRU left and right provide data to their respective MMR (1 or 2). The MMRs use ADIRU data for system initialization and to aid in operations during periods of low satellite coverage
Are the FMCs independent of one another? Do they compare information?
Yes and yes
With the FMC source select switch in NORMAL, the left FMC is primary by default, controlling the CDUs and providing input to the auto throttle. The right FMC operates in sync with the left. Although you can enter info into either MCDU, the primary FMC is responsible for syncing info with the secondary FMC and updating both MCDU displays.
The FMCs use the same air data source as the DFCS (digital flight control system, I.e combination of autopilot, auto throttle, flight director, speed trim system, Mach trim system, mode control panel, both flight control computers, and actuators into the flight controls)
FCC A gets ADR data form the left ADIRU and vice versa. If FCC A is engaged, the FMCs use ADR data from the left ADIRU and vice versa.
Usually, the FMCs receive inertial data from their on side ADIRU. If the on side ADIRU malfunctions (or in ATT or ALIGN) the FMC uses data from the other ADIRU.
With dual FMC installation, one FMC is always designated primary. Controlled by the FMC Source Select Switch.
The primary FMC:
-allocates navaid tuning and updating functions between FMCs
-ensures synchronization between FMCs
-controls MCDU displays
-provides input to the autopilot
-provides input to autothrottle
-processes ACARS datalink messages
The second FMC serves as backup and provides complete NAV functions of the other fails.
Where do FMCs receive their inertial data from?
Usually, from their on side ADIRU. Left ADIRU to FMC1 and right ADIRU to FMC2.
If on side ADIRU malfunctions (or it’s in ATT or ALIGN) the FMC uses data from the other ADIRU
What’s the criteria for airports to be included in the NAV database?
All destinations, alternates, and frequently used charter/MX locations included.
Others added as deemed reasonable, complying with:
-at least one paved runway
-at least one runway at least 5000 ft long
-at least one runway at least 100 ft wide
-at least one instrument approach. (Exceptions apply for operational needs)
How can takeoff thrust be derated?
REDUCED THRUST TAKEOFF
Reduced thrust takeoffs lower EGT and extend engine life. Used whenever perf limits/noise abatement procedure allow.
Takeoff Derate
-can be selected on N1 LIMIT page. AFM
-with derated t/o selected, thrust setting considered a limitation. Thrust levers should not be advanced further unless emergency.
—further increase following Eng failure could result in loss of directional control on the ground.
-can be further reduced by assumed temp
Assumed Temp Thrust Reduction T/O
-T/O thrust less than full rated achieved using assumed temp higher than actual temp.
-desired temp selected: SEL TEMP on N1 LIMIT page or TAKEOFF REF page 2
*max authorized 25% below cert rating
*don’t use if contaminated or wind shear
*when assumed temp is applied to full rate thrust, if needed, can apply full thrust
What sources do the FMCs use to determine position? In what order?
-GPS
-IRS
-External (ground based)
Updating priority is based on the availability of valid data from the supporting systems
FMC logic selects GPS as primary. If all GPS lost, FMC reverts to radio or IRS updating
On ground, FMC uses GPS, if not, IRS
In flight continuously updated from GPS, NAV radios, and IRS. Priority based on data from supporting systems.
FMC position from NAV sensors updates in priority order:
-GPS
-two or more DME stations
-one VOR with co-located DME
-one localizer with co-located DME
-one localizer
*DME updating defaulted to off
What criteria must be met for LNAV engagement?
LNAV engages when laterally within 3 nm of the active route leg
If outside 3 nm of active leg, LNAV engages if on an intercept heading of 90 degrees or less and intercept will occur before the active waypoint.
How does the FMC calculate a descent path during a VNAV PTH descent?
VNAV performs descents using pitch control to maintain a vertical path or target airspeed. Thrust usually commanded to idle.
Computer prior to T/D and frozen until pilot makes changes such as :
-lateral route modification
-Chang speed/altitude constraint
-change speed in FMC
Path not adjusted/recomputed even if:
-aircraft above/below the path
-airspeed too fast/slow
-speed intervention used
Modifications made during descent, FMC follow old path til new calculated. May cause VNAV disconnect (CWS PITCH) if not calculated within 60 seconds. Or, result in unattainable path changes.
End of descent point
-descent path calc projects up from end of descend (E/D) point to the cruise alt.
— based on speed/alt restrictions
—shown as green open circle labeled E/D and is last of following not proceeded by discontinuity
——rwy threshold for approaches with runway waypoint on active RTE LEGS page
——missed approach point for approaches not showing runway waypoint on active RTE LEGS page
——the lowest “at” altitude if no arrival procedure entered
*if no terminal procedure entered, FMC assumes a computed profile to 1000’ above field. FMC will provide slowdown for approach.
*VNAV path not avail of no E/D point
