Enhancing Quality Management in the Aviation MRO Sector:Integrating Lean, TQM, Six Sigma, and Emerging Digital Technologies

 In the aviation maintenance, repair, and overhaul (MRO) industry, fulfilling customer imperatives for exceptional quality and accelerated lead times remains a cornerstone of competitive advantage. Amid persistent global market volatility—exacerbated by supply chain disruptions, geopolitical tensions, and inflationary pressures—MRO providers must continually refine their strategies to navigate forecasting uncertainties. Lean principles continue to serve as a resilient operational paradigm, particularly effective in mitigating economic instability and countering escalating global competition.

The global economy's expansion is fuelling unprecedented demand for air travel. As of June 2025, the International Air Transport Association (IATA) projects passenger traffic growth to moderate to 5.8% year-over-year in 2025, down from 10.6% in 2024, yet still surpassing global GDP growth rates. This trajectory anticipates over 4.8 billion passengers annually by year-end, driven by recovering international routes in Asia-Pacific and the Middle East. For fleet-dependent airlines, maintenance expenditures now constitute up to two-thirds of an aircraft's lifecycle cost and 10–20% of total operating expenses (Syltevik et al., 2018). Sectoral expansion is amplifying these pressures: the global MRO market reached $114 billion in 2024 and is forecasted to hit $119 billion in 2025—a 12% increase over the 2019 pre-pandemic peak—before expanding at a 2.7% compound annual growth rate (CAGR) to $156 billion by 2035 (Oliver Wyman, 2025). This growth aligns with a 32% fleet expansion to 38,309 aircraft by 2035, fueled by narrowbody dominance (rising from 62% to 68% of the fleet) and aging assets, with average aircraft age climbing to 13.4 years in 2025. Through rigorous empirical review, including recent industry surveys and case analyses, this revised study evaluates the evolving adoption of Lean, Total Quality Management (TQM), and Six Sigma in MRO, while incorporating contemporary advancements such as AI-driven predictive maintenance, digital twins, and sustainability imperatives for long-term viability in aerospace operations.

Quality Management Principles in Aviation

Quality management involves the structured definition, implementation, and monitoring of processes to attain organizational quality goals, with customer satisfaction as a primary metric. Quality transcends mere compliance, influencing satisfaction via reliability, service agility, and value perception (Nsien, 2020). Although not always a direct objective, enhanced customer satisfaction is linked to revenue growth and profitability.

The Analytic Hierarchy Process (AHP), pioneered by Dr. Thomas Saaty in 1980, remains a cornerstone decision-aid tool. By breaking down multifaceted decisions into pairwise comparisons, AHP synthesizes quantitative and qualitative inputs to facilitate prioritized, evidence-based outcomes (Nsien, 2020). In contemporary MRO contexts, AHP is increasingly augmented with AI algorithms to handle vast datasets from sensor networks, enhancing prioritization in predictive scenarios.

Processes, Techniques, and Programs for Enhancing Quality Management in Aviation Production and Maintenance

In an intensely competitive aviation ecosystem, airlines and airports prioritize superior customer experiences to drive loyalty and revenue. Recent stakeholder shifts emphasize service over infrastructure scale, with experience quality tied to security efficacy and crisis responsiveness (Nsien, 2020). Aviation quality assurance frameworks enforce adherence to International Civil Aviation Organization (ICAO) and national authority standards across all operational facets (Rawashdeh, 2018).

Maintenance inspection regimes validate manufacturer protocols, overseen by certified Aircraft Quality Managers leading Quality Control teams. Internal Evaluation Programs audit these functions, while mandatory Quality Assurance Programs align activities with strategic imperatives, yielding tangible performance gains (Rawashdeh, 2018). Emerging 2025 trends integrate blockchain for traceability in parts certification, bolstering audit integrity amid supply chain volatilities.

Total Quality Management (TQM)

TQM's deployment has propelled organizational excellence by ensuring high-caliber deliverables that meet stakeholder needs, cultivating enduring success. Defined as a holistic, customer-centric strategy, TQM harnesses universal employee involvement to refine products, services, and processes (Nsien, 2020). As a philosophy of perpetual enhancement, it underpins modern Quality Management Systems, now evolving with data analytics for real-time quality dashboards.

Core Elements of TQM

End-user perceptions calibrate quality benchmarks in aviation services. Organizational success demands collective employee dedication, thriving in psychologically safe, innovative cultures (Syltevik et al., 2018). High-performance ecosystems leverage iterative improvements, with each contributor advancing shared aims to propel industry progress (Nsien, 2020). In 2025, TQM incorporates ESG (Environmental, Social, Governance) metrics, aligning quality with sustainable practices like waste minimization in maintenance workflows.

Lean Principles in Aviation Management

Lean methodology systematically eradicates waste in processes, amplifying efficiency and customer value. By excising non-essential activities, it elevates quality and throughput (Syltevik et al., 2018). Aviation's precision demands render Lean indispensable, targeting disruptions like delays and lost baggage—often rooted in procedural redundancies rather than externalities.

McKinsey & Company identifies gate delays, asset underutilization, and personnel downtime as cost amplifiers (Agyeman, 2021). Lean's toolkit, now fused with AI for dynamic waste detection, yields profound mitigations:

a) Customer Service

Self-service innovations expedite check-ins, yet agent variability—up to 50% in processing durations—persists (Syltevik et al., 2018). Digital Lean standardizes via AI-optimized workflows, curbing inconsistencies (Agyeman, 2021).

b) Delayed Departures

Boarding bottlenecks from redundancies are dissected into timed sub-processes, supplanting estimates with empirical data for streamlined executions (Agyeman, 2021). Recent 2024-2025 adoptions in European MROs have slashed turnaround times by 15-20% through AI-enhanced Lean simulations.

c) Data Collection

Baseline metrics on flows, incidents, and feedback illuminate inefficiencies. Augmented by IoT sensors, this informs precision interventions (Syltevik et al., 2018). A 2025 benchmarking study of Indian aerospace firms highlights Lean's strategic pivot toward AI integration for 25% waste reductions.

Six Sigma in Aviation

Six Sigma empowers aviation stakeholders to fortify safety, curtail costs, and amplify satisfaction via data-centric defect minimization. Its lexicon bridges leadership and operations, while its arsenal resolves process variances (Kaushal, 2021). As a continuous improvement engine, Lean Six Sigma (LSS) synergizes with AI to sustain quality amid customer exigencies (Kaushal, 2021; Hong et al., 2019).

Pivotal applications encompass:

a) Departure Processes

LSS granularizes boarding, yielding objective timings to excise redundancies, shortening cycles (Kaushal, 2021; Hong et al., 2019). A 2025 U.S. Air Force case reduced installation wastage by 30% via LSS-AI hybrids, averting delays.

b) Aircraft Maintenance

Prompt MRO safeguards revenues, as idled fleets erode yields. LSS initiatives include real-time status portals, workflow orchestration, scheduling optimization, analytics-driven refinements, and resource allocation—now AI-augmented for 10-20% efficiency gains (Hong et al., 2019; Kaushal, 2021). Boeing's 2024 LSS deployment in engine overhauls integrated AI for predictive defect detection, cutting unscheduled events by 25%.

c) Passenger Satisfaction

LSS equips crews with collaborative tools and CTQ derivations from stakeholder inputs, transforming grievances into enhancements (Kaushal, 2021). 2025 surveys indicate LSS-AI fusions in frontline training boost satisfaction scores by 15%.

Contemporary Concepts in Aviation MRO Quality Management

Beyond foundational methodologies, 2025 heralds transformative integrations of digital and sustainable paradigms, amplifying Lean, TQM, and Six Sigma.

a) Digital Twins and Predictive Maintenance

Digital twins—virtual replicas mirroring physical assets—revolutionize MRO via real-time simulation and prognostics. Leveraging IoT and AI, they forecast failures, optimizing schedules, and curtailing downtime by 20-30% (Infosys BPM, 2025). Implementation entails data ingestion, 3D visualization, scenario modeling, and iterative feedback. Rolls-Royce's engine twins exemplify 15% cost savings; Boeing's 787 battery monitoring averts risks; Airbus A350 optimizations enhance sustainability (Infosys BPM, 2025). A 2023 McKinsey survey of 45 MRO leaders reveals 56% prioritizing predictive tools, with frontrunners reporting 10% productivity surges and 10-20% spend reductions, though data silos and talent gaps hinder scale (only 6% fully integrated) (McKinsey, 2024).

b) AI Integration with Lean Six Sigma

AI augments LSS for hyper-precise analytics, automating anomaly detection and job sequencing. 2025 deployments in MROs yield 30% fewer unplanned maintenance, per airline reports (Vofox, 2025). McKinsey notes AI's role in reliability engineering, with 70% of executives anticipating criticality by 2028 (McKinsey, 2024). Challenges include legacy data and resistance, mitigated by user-centric pilots.

c) Sustainability Imperatives

Net-zero ambitions by 2050 demand MRO evolution, with ICAO's 5% intensity cut by 2030 strained by SAF shortages and older fleets (World Economic Forum, 2025). Opportunities lie in lifecycle extensions via repairs, waste reductions, and reskilling for multi-fuel tech—needing 480,000 technicians by 2026. Recommendations encompass AI for efficiency, resilient designs, and collaborative financing (World Economic Forum, 2025). OEMs like Safran advance green materials in landing gear, aligning TQM with ESG for 20% emissions cuts (Aviation Week, 2025).

Conclusion

The synergistic adoption of TQM, Lean, and Six Sigma, interwoven with digital twins, AI, and sustainability frameworks, is pivotal for advancing quality management in aviation MRO. These approaches elucidate outsourced needs via surveys and QFD, forging resilient solutions. As MRO nears $119 billion in 2025 amid fleet modernization and tech infusions, future inquiries must probe implementation hurdles, AI-LSS synergies, and net-zero trajectories in emerging markets.

Author: GR Mohan

Safety Concerns on Airbus A320 Family: An Overview

Background

The in-flight upset recently experienced by a JetBlue aircraft, followed by the Emergency Airworthiness Directive (EAD) that led to the temporary grounding of several A320-family jets, has triggered renewed concerns within both the aviation community and the travelling public regarding emerging safety risks in airline operations.

Since its inception in 1970—founded expressly to challenge the dominance of established U.S. manufacturers—Airbus has embraced a philosophy of continuous innovation and iterative product improvement. This ethos has not only driven technological progress but also fostered a proactive approach to operational safety. Its Safety Beyond Standard (SBS) approach exemplifies this ethos: a framework in which Airbus implements enhancements that exceed regulatory requirements, using real-world data, fleet feedback, and incremental software evolution—such as ELAC standard upgrades—to reinforce safety margins over the aircraft’s service life.

Role of ELAC in the A320 Fly-By-Wire (FBW) Architecture

The Elevator and Aileron Computer (ELAC) serves as a core subsystem in the Airbus A320 family's fly-by-wire flight control architecture, primarily managing pitch (via elevators) and roll (via ailerons) control laws. ELACs process pilot side-stick inputs or autopilot commands, compute deflection orders for primary flight control surfaces, enforce flight envelope protections (such as alpha protection and bank angle limits), and apply actuator gating to prevent erroneous outputs. The A320's FBW system incorporates multiple redundant flight control computers—two ELACs, three Spoiler and Elevator Computers (SECs), and two Flight Augmentation Computers (FACs)— enabling seamless transitions between Normal, Alternate, and Direct laws during failures. This redundancy ensures continued safe operation even with single or multiple failures, with ELACs handling high-integrity computations critical to maintaining structural limits and preventing loss-of-control incidents.

Hardware Families and Naming Conventions

ELAC hardware is categorised into families such as ELAC A and ELAC B, reflecting evolutionary revisions introduced by Airbus over the A320's service life to support enhanced data loading, improved processing capabilities, and compatibility with newer software standards. ELAC A represents earlier baseline hardware, while ELAC B—prevalent in modern A320ceo and A320neo fleets—incorporates upgraded boards and processors for features like modular data loading via the aircraft's Central Maintenance System (CMS). Hardware part numbers (PNs) and board revisions dictate software compatibility; for instance, only ELAC B units with specific PNs (e.g., those post-2018 production) can host advanced standards like L104. Thales Avionics, the primary ELAC manufacturer, notes that ELAC B's architecture includes dual-processor lanes for internal redundancy, but vulnerabilities in memory pathways have been highlighted in recent analyses.

Software Standards and Versioning

Airbus denotes ELAC software through "standards" (STD) labels, such as L97, L99, L103+ and L104, each encapsulating distinct feature sets, protection algorithms, and certification baselines. These versions evolve to address fleet harmonisation, NEO-specific accommodations (e.g., updated engine thrust profiles), and safety enhancements. L97 and earlier provided foundational Normal/Alternate/Direct laws with basic envelope protections. L99, rolled out around 2016-2018, introduced NEO compatibility and refined failure-handling logic. L103+ emerged as a stable interim baseline, widely validated by EASA for serviceability. L104, part of the "Safety Beyond Standards" initiative, added advanced features like Pitch Attitude Limitation in Alternate Law (PALAL) and enhanced envelope availability to mitigate loss-of-control risks. Software loading requires Airbus-approved tools and traceability to ensure DO-178C compliance.

Key Historical Milestones 

a) Early Deliveries (1988-2000s): Initial A320ceo fleets featured baseline ELAC software with core FBW laws and protections, certified under JAR-25 standards. Focus was on proving the revolutionary fly-by-wire concept.

b) STD L99 (2016-2018): Aligned CEO and NEO variants for consistent control behaviours, incorporating service bulletins for updated protections amid growing fleet diversity. This era saw over 1,000 aircraft retrofitted.

c) L103+ Baseline (2019-2024): Adopted as the primary serviceable standard, emphasising reliability and minor refinements. EASA guidance positioned it as the "gold standard" for pre-L104 fleets.

d) L104 Introduction (2024-2025): Rolled out under Airbus's proactive safety enhancements, adding PALAL, unitary VCAS monitoring at liftoff, and

modifications to prevent dual aileron/IRS losses during take-off. Installed on

approximately 6,000 aircraft (both CEO and NEO), it aimed to exceed baseline

safety margins but was suspended following the 2025 incident.

The 2025 L104 Issue and Regulatory Response: Why L103+ Was Re-
Mandated

On October 30, 2025, JetBlue Airways Flight B6-1230 (A320-200, N605JB) experienced an un-commanded pitch-down while cruising at FL350, approximately 70 nautical miles southwest of Tampa, Florida, en route from Cancun (CUN) to Newark (EWR). The aircraft descended rapidly to around 20,000 feet, injuring at least three passengers and two crew members before a precautionary diversion to Tampa International (TPA). Preliminary investigations by Airbus, the NTSB, and FAA traced the event to data corruption in an ELAC B unit running L104 software, likely triggered by a single-event upset (SEU) from intense solar particle radiation during an X5.1-class solar flare on November 11, 2025—part of heightened solar maximum activity. Corrupted memory led to erroneous elevator commands, risking structural exceedance.

In response, Airbus issued Alert Operators Transmission (AOT) A27N022-25 on November 28, 2025, followed by EASA Emergency Airworthiness Directive (EAD) 2025-0268-E, effective November 29, 2025. The EAD mandates replacement or modification of affected ELAC B L104 units with serviceable L103+ equivalents "before the next flight," allowing limited ferry flights (up to three cycles, non-ETOPS, no passengers) for positioning. The FAA and other regulators adopted similar measures. EASA cited the potential for "hazardous control outputs" as the unsafe condition, emphasising conservatism to restore predictable FBW behaviour. Airbus CEO Guillaume Faury stated: "Safety is our number one and overriding priority... We apologise for the inconvenience caused."

Practical Operational Consequences

The directive impacted roughly 6,000 A320-family aircraft (∼60% of the global fleet of 10,000+), spanning A319, A320, and A321 CEO/neo variants with specific serial numbers and PNs. Compliance involves either a 2-4 hour software reversion to L103+ (for ∼75% of units) or 3-14 day hardware swaps (for ∼25%, due to board incompatibilities). Airlines like American, Lufthansa, IndiGo, and Air India reported hundreds of cancellations and delays during the 2025 Thanksgiving period, with over 5,000 aircraft restored by November 30. Pakistan International Airlines (PIA) and Thai Airways confirmed unaffected fleets, avoiding disruptions. Operators prioritised high-utilisation aircraft per Airbus guidance, with fleet-wide analytics correlating events to solar activity and polar routes.

L103+ was selected for its proven resilience, lacking the L104-specific memory pathway vulnerability observed in heavy-ion modelling.

Technical Brief: What ELAC B L105 Must Achieve

Objective: L105 must retain and augment L104's safety enhancements (e.g., PALAL, envelope protections) while proving robustness against single-event effects (SEEs) from solar/cosmic radiation, achieving DO-178C DAL A certification with quantified radiation hardening. This addresses EASA's post-incident emphasis on environmental resilience, targeting residual failure-in-time (FIT) rates below 10^-9 per flight hour.

1. Functional & Safety Requirements (Must-Have)

a) Parity with L104: Preserve features like PALAL, VCAS monitoring, and dual failure prevention; ensure backward compatibility via traceable design matrices.

b) Deterministic Fail-Safe: Mandate predefined responses (e.g., lane dropout, law degradation, ECAM alerts) for integrity faults, avoiding non-determinism.

c) No Hazardous SEE Outputs: Single bit-flips/SEUs must not propagate to actuators; validated via fault trees showing <1% undetected hazard probability. 

(Rationale: Derived from EAD 2025-0268-E and NTSB preliminary reports on the JetBlue event.)

2. Software & Architectural Measures for Resilience

a) Redundancy & Diversity

i. Implement Triple Modular Redundancy (TMR) on ELAC B processors or

dual-lane voting with independent watchdogs.

ii. Employ design diversity for voting-critical paths to mitigate common-mode failures.

b) Memory & Data Integrity

i. Mandate ECC (Error-Correcting Code) RAM with single-bit correction/double-bit detection across critical memory.

ii. Integrate periodic scrubbing (e.g., every 10ms) and redundant state copies with cyclic voting.

iii. Require runtime CRC/hash checks on boot images and protection tables.

3. Command Gating & Plausibility

a) Enforce multi-layer filters: Cross-check commands against air data (IAS, AOA), G-loads, and configuration (flaps, gear); apply rate limits (e.g., <5°/sec elevator slew).

b) Use temporal redundancy: Re-execute high-risk computations with jitter and compare outputs.

4. Adaptive Modes

a) Trigger SEU-aware escalation: Increase scrub rates on error trends; revert to L103+ parity if >3 uncorrectable/hour, with autopilot safeguards.

(These align with DO-254 hardware hardening and post-2025 solar storm analyses.)

Diagnostics, Telemetry & Maintenance

a) Logging: Non-volatile storage for ECC events, voting discrepancies, and boot hashes; retain 1,000+ cycles.

b) Counters: Auto-generate MEL alerts on thresholds (e.g., 10 SEUs/flight); integrate with ACARS for real-time offload.

c) Analytics: Fleet-level correlation to solar indices (e.g., NOAA GOES data) and hotspots (polar/high-altitude routes).

Human Factors & Crew Procedures

a) ECAM/Annunciators: Phased messages, e.g., "ELAC B CH2 DEGRADED – ALT LAW; QRH ELAC-1," with voice alerts for upsets.

b) QRH/Training: Updated checklists for un-commanded inputs or AP disconnects; simulator scenarios mimicking solar-induced transients, per ICAO Doc 9683.

Testing & Certification Regimen

a) Software Verification

i. Full DO-178C DAL A compliance: MC/DC coverage >100%, formal methods (e.g., SPARK Ada) for supervisory kernels.

b) Fault-Injection & Radiation Testing

i. Heavy-ion/proton beam tests (LET >100 MeV·cm²/mg) at facilities like CERN or TAMU to quantify cross-sections; target <10^-7 errors/bit-day.

ii. SEU injections across RAM, buses, and ARINC 429 links; 100% detection/mitigation required.

iii. DO-160G Sections 16/20/21 for EMI/HIRF, plus high-altitude thermal/vacuum simulations.

c) System & Flight Validation

i. Hardware-in-the-loop (HIL) with injected faults; no hazardous outputs in 10^6 Monte Carlo runs.

ii. Phased flight tests: 1,000 hours initial, scaling to 10,000 with zero incidents before rollout.

(EASA will demand test reports proving L105 immunity to L104's failure mode.)

Backwards Compatibility & Deployment

a) Matrix: Document PNs supporting L105 (e.g., ELAC B rev. 3+ with ECC mods) vs. swap-required (rev. 1-2).

b) Phased Rollout: Lab validation → 100-aircraft trial → full fleet by Q3 2026; atomic swaps with <1-hour rollback to L103+.

c) Mechanisms: Signed OTA updates via CMS; BIT (Built-In Test) for post-load integrity.

Deliverables for Acceptance

a) Safety case: FHA, FMEA, CCA with radiation-specific hazards.

b) DO-178C/DC artifacts; formal proofs for gating logic.

c) Test reports: Cross-section data, FIT projections (<1 FIT/module).

d) Procedures: QRH/ECAM revisions, sim syllabi, retrofit schedules (e.g., serials 5000+ prioritized).

e) Fleet plan: Hardware swaps for ∼1,500 units by mid-2026.

Minimal On-Aircraft Failure Behaviour

Failure Type	Response	Crew Notification
Single ECC Corrected	Log; continue	None
Single Uncorrectable (1 Lane)	Drop lane; vote remainder	Caution ECAM
Cross-Lane Mismatch	Degrade to ALT/DIR Law; AP disengage	Warning ECAM + Master Caution
Repeated (>5/hour)	Ground; MEL dispatch inhibit	Critical ECAM; QRH mandatory

Acceptance Checklist (One-Page Summary)

a) L105 feature traceability to L104 (matrix complete).
b) ECC/TMR implemented & verified.
c) Heavy-ion tests: Cross-section <10^-7 cm².
d) 100% SEU mitigation in injections.
e) Formal verification of SIM/voting.
f) DO-178C DAL A artifacts (traceability, coverage).
g) Rollback validated (<30 min MTTR).
h) ECAM/QRH/training ready.
i) Telemetry pipeline live.
j) Compatibility matrix & swap plan published.

Recommended Roadmap (Rapid Deployment)

a) Immediate (Q1 2026): Core stack (ECC, scrubbing, boot security); lab verification.
b) Next (Q2 2026): SIM/voting/gating; fault injections.
c) Then (Q2 2026): Radiation/DO-178C testing.
d) Trial (Q3 2026): 100-fleet rollout with monitoring.
e) Full (Q4 2026): Global deployment; revert capability to L103+.

This L105 baseline positions the A320 fleet for sustained safety amid increasing solar activity, balancing innovation with proven resilience.

Author: GR Mohan

GNSS Interference in Aviation (Part II) Operational Checklists

 Recommended Operational Checklists for Pilots During GPS Interference

Pre-Flight Preparation

a) Review NOTAMs for GNSS interference zones along the planned route and destination.​

b) Prepare and load non-GNSS-based approaches (e.g., ILS, VOR/DME procedures) into the FMS.​

c) Verify navigation database validity to ensure alternate procedures are available.​

In-Flight Response to GNSS Loss

a) Monitor cockpit warnings such as “NAV GPS x FAULT,” “GPS PRIMARY LOST,” or “NAV GNSS x FAULT” for initial detection.​

b) Do not manually deselect GPS; allow the FMS to attempt automatic reacquisition when in a non-interference area.​

c) Switch navigation source to VOR/LOC/DME or use raw data monitoring on PFD/ND for positional information.​

d) Maintain aircraft control and use last known reliable heading; climb to a safe altitude if terrain clearance is required.​

e) Notify ATC immediately using standard ICAO phraseology, such as: “UNABLE GNSS POSITION – USING ALTERNATE NAVIGATION”.​

f) Report loss of ADS-B OUT capability if applicable.​

g) Request radar vectors or navigation assistance from ATC.​

h) Use visual references, charts, and terrain databases to supplement navigation.​

i) If RNAV is lost or position integrity errors (RAIM faults) arise, reset navigational sources and continue using published procedures or ATC direction.​

j) Disable GNSS position updates and terrain look-ahead functions if persistent nuisance alerts occur.​

Post-Flight Actions

a) Log GNSS interference events in the tech log, with time, location, and phase of flight.​

b) File a report with safety departments or regulatory authorities (DGCA, ICAO, FAA, or IATA as relevant).​

c) Coordinate with maintenance for follow-up and engineering checks.​

Example ICAO/EASA GNSS Loss Checklist (Summary Table)

Phase	Task	Reference
Pre-Flight	Check NOTAMs for GNSS RFI	​
Pre-Flight	Load non-GNSS approaches (ILS/VOR/DME)	​
In-Flight	Monitor for GNSS fault alerts	​
In-Flight	Switch to alternate navigation sources	​
In-Flight	Notify ATC, request radar vectors if needed	​
In-Flight	Use visual/terrain references	​
Post-Flight	Log the event, time, phase, details	​
Post-Flight	File report to authorities	​
Post-Flight	Notify maintenance for tech follow-up	​

In addition, always ensure enhanced crew briefing for GNSS contingency scenarios, include diversion airports with conventional navigation capability, and maintain readiness for real-time reporting as per regulatory mandates (e.g., DGCA's 10-minute requirement in India).

Cockpit Flow for GNSS Failure

1. Detect GNSS Failure

2. Observe GNSS/FMS warnings (“GPS PRIMARY LOST,” “NAV GNSS FAULT,” map shifts, or abnormal alerts such as unintended TAWS).​

3. Confirm and Cross-Check

4. Verify loss using standby/alternate navigation sources (e.g., IRS, radio nav aids, or visual references).​

5. Switch to Alternate Navigation

6. Select appropriate alternative (ILS, VOR/DME/LOC, INS) and update navigation mode on FMS and PFD.​

7. Advise ATC

8. Inform Air Traffic Control with standard phraseology (“UNABLE GNSS POSITION – USING ALTERNATE NAVIGATION”).​

9. Notify loss of ADS-B if applicable.

10. Maintain Situational Awareness

11. Use charts and visual references as needed.

12. Request radar vectors if required.​

13. Continue With Published Non-GNSS Procedures or ATC Guidance

14. Follow pre-briefed conventional approach or ATC instructions for routing/diversion.​

15. Log Event

16. Record occurrence details and report per regulatory requirements after landing.​

This flow ensures safe reversion to alternate procedures and effective coordination with air traffic control during declared GNSS outages.

Steps for Immediate Actions to Maintain Aircraft Control

Immediate actions to maintain aircraft control after GNSS (GPS) loss are focused on preserving situational awareness, ensuring safe flight operation, and reverting to reliable backup systems. The following steps are recommended:

Immediate Actions After GNSS Loss

a) Maintain Attitude and Heading
Monitor and trust primary flight instruments (attitude indicator, heading indicator, airspeed, and altimeter) for aircraft control. Do not attempt major navigational changes while diagnosing the failure; stabilize flight first.​

b) Cross-Check Navigation Inputs
Confirm loss using alternate sources such as inertial navigation systems (IRS/INS), radio navigation (VOR, DME, LOC), and visual references if available. Compare readings to identify false or drifting indications.​

c) Switch to Alternate Navigation
Select and activate ground-based navigation aids or inertial systems as primary reference. Update FMS or PFD to display conventional navigation data.​

d) Inform ATC Immediately
Declare "GNSS failure" to Air Traffic Control, stating your position based on the last known fix and current method of navigation. Request radar vectors or navigation assistance if needed.​

e) Monitor Terrain and Traffic
Ensure safe altitude and position especially in proximity to terrain and controlled airspace. Follow published minimum safe altitudes and use visual or radio references to avoid obstacles.​

f) Reduce Cockpit Workload
Prioritize essential flying tasks, minimize secondary activities, and delegate duties. Stay focused on aircraft control and navigation.​

This sequence preserves safe flight trajectory, quickly adapts navigation sources, and aligns communications for ongoing flight safety during a GNSS outage. Always follow company-specific and aircraft-manufacturer procedures where applicable.

Immediate ATC Calls to Make After GNSS Loss

After GNSS loss, the recommended immediate ATC calls focus on declaring the situation, ensuring operational safety, and enabling support from air traffic controllers. Use the internationally standard phraseology and concise reports:

Immediate ATC Calls After GNSS Loss

1. Declare GNSS Failure:
“UNABLE GNSS POSITION – USING ALTERNATE NAVIGATION”
This informs ATC that GPS-based navigation is lost and you are reverting to alternative means such as VOR, DME, INS, or radar vectors.​

2. Report Location and Situation:
State your aircraft’s last reliable position, present navigation method, and intentions.
Example: “ATC, [Callsign], unable GNSS position after [position], now using VOR/DME, request radar vectors”.​

3. Report Loss of Surveillance Capabilities (if applicable):
If ADS-B OUT is lost due to GNSS failure, immediately notify ATC:
“ATC, [Callsign], ADS-B OUT unavailable due to GNSS loss”.​

4. Request Assistance:
Request radar vectors, alternate clearances, or emergency support if required for terrain or traffic separation.​

5. Follow Regulatory Reporting Protocol:
As per DGCA and ICAO, file a mandatory real-time report (within 10 minutes in India) on the GNSS interference event through official channels.​

Note: Always use clear, internationally recognized phraseology and promptly communicate navigation impairments to ensure safety and regulatory compliance.

Declare UNABLE RNP phraseology to use with ATC

a) The standard ICAO-compliant phraseology for declaring inability to meet RNP requirements due to GNSS loss is:

"UNABLE RNP"

b) If needed, this can be clarified further with the cause:

"UNABLE RNP DUE TO GNSS FAILURE"

c) You may also expand using structured phraseology per the situation, for example:

“UNABLE RNP ON PRESENT STAR, REQUEST RADAR VECTORS”

“UNABLE RNP FOR APPROACH, REQUEST ALTERNATE CLEARANCE”

d) Declare this to ATC as soon as the UNABLE RNP alert appears in the cockpit, ensuring controllers understand the situation and can provide vectors or alternative navigation clearances.

Differences between UNABLE RNAV and UNABLE RNP

The key differences between “UNABLE RNAV” and “UNABLE RNP” phraseology relate to the underlying navigation requirements and what ATC should infer about the aircraft’s capability:

1. “UNABLE RNAV” Phraseology

a) Meaning: The aircraft cannot perform any area navigation (RNAV) per the current clearance, often due to equipment failure or database issues.

b) Pilot Action: State "UNABLE RNAV" to ATC and request radar vectors or conventional navigation alternatives (like VOR or DME routes).​

c) Implication: The aircraft must revert to traditional navigation methods, and ATC may assign conventional procedures or vectors.

2. “UNABLE RNP” Phraseology

a) Meaning: The aircraft cannot guarantee the specific Required Navigation Performance (RNP) level for the leg or procedure, often due to GNSS loss, RAIM issue, or onboard performance monitoring alerting.

b) Pilot Action: State "UNABLE RNP" with the reason (e.g., "UNABLE RNP DUE TO GNSS FAILURE"), clarify if area navigation can still be performed by other means, and request appropriate instructions.​

c) Implication: Loss of RNP does not always mean complete area navigation loss—alternate positioning sources (e.g., DME/DME) may still allow navigation, but not with the required RNP precision. ATC may need to assess whether vectors, alternate clearances, or contingency measures are necessary.

Phraseology	Description	Typical Cause	ATC Response
UNABLE RNAV	Unable to use area navigation as cleared	Equipment or database failure	Assign vectors or conventional SID
UNABLE RNP	Unable to meet the RNP for the procedure	GNSS/RAIM issue or alert	Clarify alternate nav capability, assign vectors or alternatives as needed

In essence,

“UNABLE RNAV” indicates total loss of area navigation capability, while

“UNABLE RNP” indicates a performance shortfall on a specified RNP operation, possibly with other navigation methods still available.​

Author: GR Mohan