Under what conditions may the marker beacon receiving system be inoperative for IFR operations?

The marker beacon (item 34-31-1A) may be inoperative under IFR operations provided approach procedures do not require marker fixes.

What are the dispatch conditions for an inoperative ILS or MLS under IFR?

The ILS (or MLS) (item 34-32-1A) may be inoperative under IFR operations provided that any approaches or missed approaches in which navigation is based on ILS are not included in the flight plan.

What conditions must be met to dispatch with an inoperative Airborne Collision Avoidance System (ACAS)?

The ACAS (item 34-40-1A) may be inoperative provided (a) the ACAS is deactivated, and (b) operating procedures do not require its use. Procedures: (O) to provide alternate crew procedures, as applicable; (M) to provide guidance for deactivation of the ACAS.

When may the combined TA and RA dual display be inoperative on the pilot monitoring's side?

The combined TA and RA dual display (item 34-40-1-1A) may be inoperative on the pilot monitoring's side provided (a) TA and RA elements and audio functions are operative on the pilot flying's side, and (b) TA and RA display indications are visible to the pilot monitoring. Procedures: (O) to provide alternate crew procedures, as applicable.

What are the conditions for dispatching with an inoperative Area Navigation System?

The Area Navigation System (item 34-40-2A) may be inoperative provided (a) applicable airspace requirements for the intended flight route are complied with, (b) certified RNP/RNAV capabilities relevant for the intended flight route are maintained, and (c) operational procedures do not require its use. Procedures: (O) to provide information about which procedures require its use and to provide alternate navigation procedures, if applicable.

Under what conditions may the weather detection system be inoperative when no thunderstorm is forecast?

The weather detection system (item 34-41-1C) may be inoperative provided no thunderstorm or other potentially hazardous weather conditions, regarded as detectable with the airborne weather detection system, are forecasted along the route. The route corresponds to any point on the route including diversions to reach alternate aerodromes required by the operational rules.

What is the maximum time a Terrain Awareness Warning System (TAWS) may be inoperative?

The TAWS (item 34-43-1A) may be inoperative for a maximum of 6 flights or 2 calendar days, whichever occurs first.

What conditions allow dispatch with an inoperative TAWS Mode 5 (Glideslope Deviation)?

TAWS Mode 5 (item 34-43-1-3A) may be inoperative. Alternatively, item 34-43-1-3B allows it to be inoperative for day VMC only.

What are the conditions for dispatching with an inoperative TAWS FLTA and PDA functions?

The TAWS FLTA and PDA functions (item 34-43-1-4A) may be inoperative provided (a) Mode 1-4 are operative, and (b) approach procedures do not require its use.

What conditions apply to dispatching with an inoperative Runway Overrun Awareness and Alerting System (ROAAS)?

The ROAAS (item 34-44-1A) may be inoperative provided it is deactivated. Procedures: (M) to provide instructions on how to deactivate the system. If the ROAAS provides an automated means of deceleration control, its unavailability should be highlighted to the flight crew and eventual performance penalties applied.

Under what conditions may navigation systems based on VOR, DME, GNSS, INS be inoperative for non-commercial air transport operations?

For non-commercial air transport operations, navigation systems (item 34-51-1A) may be inoperative provided (a) operations are conducted under VFR, and (b) applicable airspace requirements are complied with.

What are the conditions for dispatching with an inoperative SSR Transponder Mode A/C?

The SSR Transponder Mode A/C (item 34-54-1A) may be inoperative for a maximum of 5 flights provided (a) flight is conducted under VFR over routes navigated by reference to visual landmarks, and (b) permission is obtained from the Air Navigation Service Provider(s) along the route or any planned diversion. Note: Mode C function is required to be operative for RVSM operations.

What conditions apply to dispatching with an inoperative SSR Transponder Mode S?

The SSR Transponder Mode S (item 34-54-2B) may be inoperative provided permission is obtained from the Air Navigation Service Provider(s) when required for the intended flight route. Note: An SSR transponder with an operative Mode S function is defined as a transponder which can provide, at least, Elementary Surveillance capability.

What is the dispatch relief for inoperative Enhanced Surveillance Functions in the Single European Sky?

One or more Downlinked Aircraft Parameters (DAPs) which provide Enhanced Surveillance (item 34-54-2-1B) may be inoperative for three calendar days. Note: Enhanced surveillance capability is required in Mode S EHS notified airspace.

What conditions apply to dispatching with inoperative Extended Squitter (ADS-B OUT) Transmissions outside the Single European Sky?

One or more extended squitter transmissions (item 34-54-2-2C) may be inoperative when required for the intended flight route.

What is the condition for dispatching with an inoperative Aircraft Tracking Equipment?

The Aircraft Tracking Equipment (item 34-55-1B) may be inoperative provided that at least one automatic emergency locator transmitter is operative.

ATA 34 NAVIGATION -- Navigation equipment

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ATA 34 NAVIGATION — Navigation equipment

ED Decision 2025/021/R

Summary of the guidance items:

ITEM	ATA
Marker Beacon (MC)	34-31-1
ILS (or MLS) (MC)	34-32-1
Airborne Collision Avoidance System (ACAS) (MC)	34-40-1
Area Navigation System	34-40-2
Weather Detection System (Antenna(s), XCVR(s), Controller(s), Display(s))	34-41-1
Wind shear Detection/Warning System (if installed)	34-41-2
Navigation Systems (based on VOR, DME, ADF, GNSS, INS)	34-51-1
Terrain Awareness Warning System (TAWS)	34-43-1
SSR Transponder Mode A/C	34-54-1
SSR Transponder Mode S	34-54-2
Aircraft Tracking Equipment	34-55-1

Aircraft applicability: Aeroplanes

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions
34-31-1	Marker Beacon (MC)
34-31-1A		C	-	0	May be inoperative under IFR operations provided approach procedures do not require marker fixes.

34-31-1B		D	-	0	May be inoperative under VFR operations.

Additional considerations:

One marker beacon receiving system is required to be installed where a marker beacon is required for approach navigation purpose.

Aircraft applicability: Aeroplanes

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions
34-32-1	ILS (or MLS) (MC)
34-32-1A		B	-	0	May be inoperative under IFR operations provided that any approaches or missed approaches in which navigation is based on ILS are not included in the flight plan.

34-32-1B		D	-	0	May be inoperative under VFR operations.

Additional considerations:

N/A

Aircraft applicability: Aeroplanes & Helicopters

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-40-1	Airborne Collision Avoidance System (ACAS) (MC)
34-40-1A		B	-	0	(O)(M) May be inoperative provided:
					(a) The ACAS is deactivated, and (b) Operating procedures do not require its use.
					Procedures: (O) To provide alternate crew procedures, as applicable. (M) To provide guidance for deactivation of the ACAS.
34-40-1B		C	-	-	(M) Any in excess of those required may be inoperative provided it is deactivated.
					Procedures: (M) To provide guidance for deactivation of the ACAS.
34-40-1-1	Combined TA and RA Dual Display
34-40-1-1A		C	-	1	(O) May be inoperative on the pilot monitoring’s side provided:
					(a) TA and RA elements and audio functions are operative on the pilot flying’s side, and (b) TA and RA display indications are visible to the pilot monitoring.
					Procedures: (O) To provide alternate crew procedures, as applicable.
(continued)

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions
(continued)
34-40-1-2	Resolution Advisory (RA) Display Systems
34-40-1-2A		C	-	1	(O) One may be inoperative on the pilot monitoring side.
					Procedures: (O) To provide alternate flight crew procedures, as applicable.
34-40-1-2B		C	-	0	(O) One or more may be inoperative provided:
					(a) All Traffic Alert (TA) display elements and voice command audio functions are operative, and (b) TA only mode is selected by the crew, and (c) Operating procedures do not require its use.
					Procedures: (O) To provide alternate crew procedures, as applicable.
34-40-1-3	Traffic Alert (TA) Display System(s)
34-40-1-3A		C	-	0	(O) One or more may be inoperative provided:
					(a) RA display and audio functions are operative, and (b) Operating procedures do not require its use.
					Procedures: (O) To provide alternate flight crew procedures, as applicable.

Additional considerations:

The deactivation of the ACAS can alternatively be performed through an operational procedure, if acceptable.

34-40-1B covers the failure of the ACAS when the system is not required by operating rules.

Aircraft applicability: Aeroplanes

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-40-2	Area Navigation System
34-40-2A		C	-	-	(O) may be inoperative provided:
					(a) Applicable airspace requirements for the intended flight route are complied with, (b) Certified RNP/ RNAV capabilities relevant for the intended flight route are maintained, and (c) Operational procedures do not require its use.
					Procedures: (O) To provide information about which procedures require its use .To provide alternate navigation procedures, if applicable.
		A	-	0	(O) May be inoperative for one flight provided:
					(a) Routing is planned via ground-based navigational aids taking account of promulgated range, and (b) Permission is obtained from the Air Navigation Service Provider(s) when required for the intended flight route.

Additional considerations:

The RNAV systems are stated in the Aeronautical Information Publications (or their equivalent) as being required to satisfy operational requirements for airspace procedures.

Additionally, the certified capability may be dependent on a number of systems which may vary from one aircraft type to another. The reference to appropriate operational documentation (Aircraft Flight Manual, FCOM, etc.) may be necessary in order to allow the dispatch, depending on the intended flight route.

Aircraft applicability: Aeroplanes & Helicopters

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-41-1	Weather Detection System (Antenna(s), XCVR(s), Controller(s), Display(s))
34-41-1A		D	-	-	Any in excess of those required may be inoperative provided procedures do not require their use.
34-41-1B		C	-	0	May be inoperative provided operations are conducted in daylight VMC.
34-41-1C		C	-	0	May be inoperative provided no thunderstorm or other potentially hazardous weather conditions, regarded as detectable with the airborne weather detection system, are forecasted along the route.
					Note: The route corresponds to any point on the route including diversions to reach alternate aerodromes required by the operational rules.
34-41-1-1	Wind shear Detection/Warning System Predictive Function
34-41-1-1A		C	-	0	May be inoperative.

Additional considerations:

ACAS item may drive the relief as the same display may be used. Refer to item 34-40-1.

ETOPS requirements are to be considered.

34-41-1-1A:

Considerations have to be taken that the failure of the predictive wind shear function may be a consequence of the loss of inputs from other items (e.g. radio altimeter). In that case, the associated guidance also applies.

Aircraft applicability: Aeroplanes & helicopters

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-41-2	Wind shear Detection/Warning System (if installed)

34-41-2-1	Reactive Function
34-41-2-1A		C	-	0	(O) May be inoperative provided alternate procedures are established and used.
					Procedures: (O) To provide guidance procedures for wind shear avoidance and wind shear recovery procedure.

Additional considerations:

The operational procedure shall be developed to:

— Assess and minimise the probability of encountering wind shear during take-off/departure and approach/landing.

— Minimise the effects of unexpected wind shear encounter during take-off/departure and approach/landing.

The above guidance has to be consolidated with the associated restrictions applicable to ground proximity warning system (GPWS) (ATA 34), weather radar system (ATA 34), flight guidance system (ATA 22) or flight director (Guidance Item 22-10-2) should the wind shear predictive or reactive function be performed by those systems.

Aircraft applicability: Aeroplanes

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-43-1	Terrain Awareness Warning System (TAWS)
34-43-1A		A	-	0	May be inoperative for a maximum of 6 flights or 2 calendar days, whichever occurs first.
34-43-1B		C	-	0	Any in excess of those required may be inoperative.
34-43-1-1	Modes 1 to 4
34-43-1-1A		B	-	0	One or more mode may be inoperative provided FLTA and PDA functions are operative.
34-43-1-2	Test Mode
34-43-1-2A		A	-	0	May be inoperative for a maximum of 6 flights or 2 calendar days, whichever occurs first.
34-43-1-3	Glideslope Deviation (Mode 5)
34-43-1-3A		B	-	0	May be inoperative.

34-43-1-3B		C	-	0	May be inoperative for day VMC only.

34-43-1-4	Terrain System- Forward Looking Terrain Avoidance (FLTA) and Premature Descent Alert (PDA) functions
34-43-1-4A		B	-	0	May be inoperative provided:
					(a) Mode 1-4 are operative, and (b) Approaches procedures do not require its use.
34-43-1-5	Advisory Callouts
34-43-1-5A		C	-	0	(O) May be inoperative provided:
					(a) Low visibility approaches requiring the use of affected callouts are not performed, and (b) Alternate procedures are established and used.
					Note: Check Flight Manual limitations for approach minima.

Additional considerations:

The above guidance is applicable to either Class A or Class B TAWS.

The mode 1-5 referenced in the guidance correspond to:

Mode 1 — Excessive descent rate (sink rate);

Mode 2 — Excessive terrain closure rate (ground proximity);

Mode 3 — Altitude loss after take-off or go around;

Mode 4 — Unsafe terrain clearance during high speed flight or while not in the landing configuration;

Mode 5 — Below glideslope deviation alert.

FLTA & PDA functions are required for RNP-AR (Required Navigation Performance (RNP) instrument approach procedures with Special Aircraft and Aircrew Authorization Required (SAAAR) operations.

Aircraft applicability: Aeroplanes

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-44-1	Runway Overrun Awareness and Alerting System (ROAAS)
34-44-1A		C	-	0	(M) May be inoperative provided it is deactivated.
					Procedures: (M) To provide instructions on how to deactivate the system.

Additional considerations:

If the ROAAS provides an automated means of deceleration control, its unavailability should be highlighted to the flight crew and eventual performance penalties applied.

The deactivation of the ROAAS can alternatively be performed through an operational procedure, if acceptable.

Aircraft applicability: Aeroplanes & Helicopters:

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-51-1	Navigation Systems (based on VOR, DME, GNSS, INS)
34-51-1A	(Except for commercial air transport operations)	D	-	0	May be inoperative provided:
					(a) Operations are conducted under VFR, and (b) Applicable airspace requirements are complied with.
34-51-1B		C	-	-	(O) One or more may be inoperative provided:
					(a) The navigation systems required for each segment of the intended flight route are operative, and (b) Alternate procedures are established and used, where applicable.
					Procedures: (O) To give alternate procedures in case existing operational procedures are affected.

34-51-2	Navigation System (ADF)	D	-	-	Any in excess of those required for the intended flight route may be inoperative.

Additional considerations:

This entry covers failure of navigation systems, e.g. VOR, DME, ADF, INS, and GNSS, that provide approved navigation information to the flight crew as either a stand-alone system or in combination with a navigation management system (e.g. FMS, R-NAV).

However, this entry does not cover the failure of navigation management system.

Others aircraft systems may be affected by the failed navigation system (e.g. TAWS). This has to be reflected on a case-by-case basis when this guidance is applied.

Heading, airspeed, and clock data are not considered as a navigation system by this guidance.

Additional restrictions may apply if required during certification of the navigation systems. As an example, if raw navigation data have been used to achieve an acceptable level of safety, in addition to any multi-sensor computed data, to avoid ‘hazardously misleading’ navigation information, further restriction on the availability of such raw data information may be required.

Operational rules for the selection of alternate aerodromes are available in operational requirements.

Aircraft applicability: Aeroplanes & Helicopters

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions
34-54-1	SSR Transponder Mode A/C
34-54-1A		A	-	0	(O) May be inoperative for a maximum of 5 flights provided:
					(a) Flight is conducted under VFR over routes navigated by reference to visual landmarks, and (b) Permission is obtained from the Air Navigation Service Provider(s) along the route or any planned diversion.
					Note: Mode C function is required to be operative for RVSM operations
34-54-1B		D	-	-	Any in excess of those required may be inoperative.
34-54-2	SSR Transponder Mode S
34-54-2A		D	-	-	Any in excess of those required for the intended flight route, may be inoperative.
					Note: A SSR transponder with an operative Mode S function is defined as a transponder which can provide, at least, Elementary Surveillance capability.
34-54-2B		C	-	0	One or more may be inoperative provided permission is obtained from the Air Navigation Service Provider(s) when required for the intended flight route. Note 1: An SSR transponder with an operative Mode S function is defined as a transponder which can provide, at least, Elementary Surveillance capability. Note 2: Elementary Surveillance (ELS) capability (Mode S including Aircraft Identification and Pressure Altitude Reporting) is required in European Mode S designated airspace. Note 3: Altitude reporting, provided by an SSR transponder Mode S function, is required for ACAS II operation. Refer to item 34-40 for flight with ACAS II inoperative. Note 4: Altitude reporting, provided by an SSR transponder Mode S function, is required for flight into RVSM airspace.
(continued)

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions
(continued)
34-54-2-1	Enhanced Surveillance Functions
34-54-2-1A		D	-	0	One or more Downlinked Aircraft Parameters (DAPs), which provide Enhanced Surveillance, may be inoperative when not required for the intended flight route.
34-54-2-1B	Operations in the Single European Sky	A	-	0	One or more Downlinked Aircraft Parameters (DAPs), which provide Enhanced Surveillance, may be inoperative for three calendar days.
					Note: Enhanced surveillance capability is required in Mode S EHS notified airspace.
34-54-2-1C	Operations outside the Single European Sky	C	-	0	One or more Downlinked Aircraft Parameters (DAPs), which provide Enhanced Surveillance, may be inoperative when required for the intended flight route.
34-54-2-2	Extended Squitter (ADS-B OUT) Transmissions
34-54-2-2A		D	-	0	One or more extended squitter transmissions may be inoperative when not required for the intended flight route.
34-54-2-2B	Operations in the Single European Sky	A	-	0	One or more extended squitter transmissions may be inoperative for three calendar days.
34-54-2-2C	Operations outside the Single European Sky		-	0	One or more extended squitter transmissions may be inoperative when required for the intended flight route.

Additional considerations:

Enhanced surveillance is not applicable to helicopters. They are only required to install elementary surveillance. This does not preclude a helicopter from voluntary installation of enhanced surveillance.

24-54-2 SSR Mode S Transponder

If ELS capability of the Mode S transponder is maintained, the 34-54-2B entry is not applicable, but reference to 34-54-2-1 enhanced surveillance functions may be required.

If ELS capability is affected, prior ANSP permission is required.

As an example, this may be achieved through the utilisation of Item 10 of the FPL that can be completed using the designator letters for the surveillance/SSR equipment element as follows:

‘S’ — Transponder, Mode S, including both pressure altitude and aircraft identification transmission. [This equates to ELS compliant]

‘P’ — Transponder, Mode S, including pressure altitude transmission but no aircraft identification transmission.

‘I’ — Transponder, Mode S, including aircraft identification transmission but no pressure altitude transmission.

‘X’ — Transponder, Mode S, without both pressure altitude and aircraft identification transmission.

‘C’ — Transponder, Mode A (4 digits - 4096 codes) and Mode C.

‘A’ — Transponder, Mode A (4 digits - 4096 codes).

‘N’ — Nil (Hardly likely to be accepted into European airspace).

From a practical ATC perspective, most probably only ‘S’, ‘P’, and ‘C’ would be acceptable to Air Navigation Service Providers (ANSPs), whilst ‘C’ would reply to ground Mode S interrogations, this level of functionality in a Mode S environment might not be acceptable to all ANSPs in the long term.

Aircraft applicability: Aeroplanes & Helicopters

ATA Chapter: 34 Navigation

(1) System & Sequence Numbers		(2) Rectification Interval
ITEM			(3) Number installed
				(4) Number required for dispatch
					(5) Remarks or Exceptions

34-55-1	Aircraft Tracking Equipment
34-55-1A		D	-	-	Any in excess of those required by regulations may be inoperative.
34-55-1B		C	-	-	May be inoperative provided that at least one automatic emergency locator transmitter is operative.

Additional considerations:

An aircraft tracking system is required for helicopter offshore operations in a hostile environment, according to SPA.HOFO.150 of Annex V (Part-SPA) to Regulation (EU) No 965/2012, and for aeroplanes under the conditions given by CAT.GEN.MPA.205 (a) of Annex IV (Part-CAT) to Regulation (EU) No 965/2012.

Details

Source-Title: ATA 34 NAVIGATION -- Navigation equipment View latest amendments

Erulesid: ERULES-1963177438-4160 Compare versions

Domain: Initial airworthiness

Amendedby: CS Issue 4

Applicabilitydate: 18 December, 2025

Entryintoforcedate: 18 December, 2025

Regulatorysource: ED Decision 2025/021/R Navigate

Regulatorysubject: CS-MMEL

Typeofcontent: GM to CS (Guidance material to certification specification)

Origin: EASA

Category: EAR