AVIA 261 INSTRUMENT LANDING SYSTEMS (ILS) - Cautions

1
AVIA 261INSTRUMENT LANDING SYSTEMS (ILS)
- Cautions

• Low Clearance Indication
• - Less than full scale deflection of CDI when
  full scale should be indicated
• - Occur gt8o from LOC centreline
• - Provides premature indication of course
  interception
• - Caused by failure of certain elements of
  antenna array
• - Never observed when lt8o from LOC centreline
• - Cure by - Cross-check other bearing info
  ADF, etc.
• - Do not initiate autopilot coupled appr until
  established on LOC centreline
• - Notify ATC of ANY abnormality within 35o of
  published Front or Back Course

2
AVIA 261INSTRUMENT LANDING SYSTEMS (ILS)
- Cautions

• Localizer False Course (False Course Capture)
• - Occurs when pilot prematurely selects APPR
  mode on A/P
• Even when all elements working to standard
• - Also premature indication of course
  interception
• - Can occur from 8o to 35o from centerline
• - Most likely from 8o to 12o
• Cure by - Use raw data to intercept course
• - Select APPR Mode ONLY when within 8o 18 NM
  of threshold
• - Cross check raw data ADF, etc
• - Be prepared to deselect re-arm A/P APPR mode

3
AVIA 261INSTRUMENT LANDING SYSTEMS (ILS)
- Cautions

• Electromagnetic Interference
• - In built up areas, from power transformer
  stations, industrial activities broadcast XMTRs
  
• - Transitory variable from receiver to
  receiver Difficult to quantify
• - New receiver standards provide better
  protection from FM interference
• Should solve most of the problems
• - Most often wont affect receivers in primary
  reception/use zone
• - Usually ATC is aware will advise pilot

4
AVIA 261INSTRUMENT LANDING SYSTEMS (ILS)
- Cautions

• False Glide Slope Signals
• - Occur in multiples of glide path angle (6o,
  9o, etc.)
• - First signal (6o) is reciprocal (Fly down -gt
  Fly up)
• - 9o signal is correctly oriented
• - No false signals below GP
• - Should not be experienced by acft flying Front
  Course ILS as published

5
AVIA 261INSTRUMENT LANDING SYSTEMS (ILS)
- Cautions

• Autoland Operations
• - Used with Auto Flight Control Guidance System
  (AFCGS)
• - Designed for use in Cat III conditions, CAT
  III operations
• - Used at other times to maintain currency
• -gt Need for CAUTION
• - Cat I II facilities OK for Cat I II
  limits, Not designed for Cat III
• - Signal areas only protected during Cat III Ops
• - ie different hold lines
• - ILS signal quality may change rapidly
  without warning
• - Pilots need to be prepared to IMMEDIATELY
  discontinue practice session