In many thousands of households located underneath the flight path of Tribhuvan International Airport (TIA), there is a common occurrence which they accept as something normal – the physical shaking of their buildings as a result of vibrations caused by aircraft taking off and landing. This problem is especially acute in the TIA zoned area. As someone who has worked throughout my career as a civil engineer, I have personally witnessed the visible damage caused by aircraft vibrations, such as cracks in walls, plaster fall-off, rattling windows, among others.
What follows below is a detailed engineering-oriented investigation into the issue, focusing on the effects of vibration by aircraft on buildings; difference between the buildings in flight corridor and those that are not; regulatory issues in the context of Nepal and finally what the government should do immediately.
1. Introduction: The Problem Nobody Officially Acknowledges
Balkumari is one of the many localities in Lalitpur district that comes under the flight approach path of Runway 02/20 of Tribhuvan International Airport. Airplanes flying in for landing pass over the locality, dropping down as low as 150 to 300 metres above ground level. For take-offs, airplanes use a steep ascent trajectory through this route using maximum engine thrusts.
In simpler terms, people living in areas such as Balkumari, Hadigaun, Gairigaun, Sinamangal, and other nearby locations face overflight passes every three to four minutes during busy hours. In situations when low-level flights are common due to weather conditions such as monsoon season where airplanes need to fly steeper to land safely, or during night time when there are cargo flights taking off and landing, the vibrations caused on the ground become more noticeable.
The most common question that people have is – am I damaging my building with this? The answer is quite interesting from an engineering point of view. Yes, in the long term, buildings will deteriorate due to vibration fatigue, especially those that are not designed to withstand dynamic loads. The majority of buildings in Nepal are not.
2. The Physics of Aircraft-Induced Ground Vibration
2.1 Sources of Vibration
Aircraft produce vibration that reaches structures through two distinct pathways:
The first is airborne noise and pressure waves. The high-decibel sound produced by jet engines particularly at low altitudes which generates pressure fluctuations in the air. These pressure waves impinge on building facades, windows, roofs, and walls, inducing resonant vibration in lightweight or poorly connected structural elements. This is most noticeable in single-pane glass windows, lightweight partition walls, and asbestos or CGI sheet roofing.
The second is ground-transmitted vibration. This is less understood by the general public. The pressure differential created by aircraft engines and the physical compression of air beneath low-flying aircraft creates ground surface vibration similar in some respects to the vibration produced by heavy trucks or rail traffic, but at different frequencies. This vibration propagates through soil and into building foundations.
2.2 Key Parameters of Concern
In structural vibration analysis, the following parameters determine damage potential:
| Parameter | Definition | Aircraft-Induced Range | Damage Threshold |
| PPV (Peak Particle Velocity) | Max ground velocity at foundation | 0.5 – 5.0 mm/s typical | 2.0 mm/s for old masonry |
| Frequency (Hz) | Cycles per second of vibration | 1 – 80 Hz (engine + airframe) | Structural resonance at 5–20 Hz |
| Sound Pressure Level (dB) | Acoustic energy impacting structure | 75 – 105 dB at approach | >85 dB sustained causes fatigue |
| Duration of Event | Seconds of exposure per flyover | 15 – 90 seconds per event | Cumulative cycles over years |
2.3 The Concept of Vibration Fatigue
A single aircraft flyover does not crack a wall. This is an important distinction that often leads people and even some engineers to dismiss the concern. The damage is cumulative and occurs through a mechanism called vibration fatigue.
Every material under cyclic stress accumulates micro-damage at a rate determined by the stress amplitude and number of cycles. Brick masonry mortar joints, cement plaster, concrete lintels, and unreinforced masonry walls are all susceptible. For example: when a building in the Balkumari corridor experiences 200 to 300 aircraft vibration events per day a conservative estimate for TIA operations and this continues for 10, 20, or 30 years, the cumulative fatigue loading on vulnerable elements is substantial.
To put this in perspective: a building that has stood in the flight corridor for 20 years has experienced approximately 1.5 to 2.5 million individual vibration loading events. No unreinforced masonry wall, no cement plaster, and no older foundation was designed for that loading history.
3. Buildings in the Flight Zone vs. Outside Flight Zone : A Structural Comparison
3.1 Typical Construction in Flight Corridor Area
Having walked through Balkumari and the surrounding wards as a local resident and structural observer over many years, I can describe the typical building stock in this corridor with accuracy. The dominant typologies are:
- Load-bearing brick masonry buildings, typically 2 to 4 storeys, built between 1970 and 2000, using fired clay bricks with traditional mud or lime-cement mortar. These are the most vulnerable category.
- Older reinforced concrete frame buildings with brick infill walls, built between 1990 and 2010, without seismic detailing and with minimal consideration for dynamic loads. These perform better under vibration but are still susceptible to infill wall cracking.
- Newer engineered RCC frame structures built post-2015 earthquake code revision, with some consideration for dynamic loading. These perform best, though acoustic fatigue remains a concern.
- Tin and CGI sheet-roofed single-storey structures, which suffer the most visibly from acoustic vibration due to the lightweight nature of the roofing material and its low natural frequency.
3.2 Visible and Measurable Damage Indicators
In buildings located directly within the primary flight corridor roughly a 500 metre wide swath on each side of the approach centreline the following damage patterns are consistently observed over time:
Plaster Cracking and Delamination
This is the most common and earliest visible sign. Plaster, being a brittle material with low tensile strength, is the first to accumulate fatigue micro-cracking. The cracks typically appear at re-entrant corners (where walls meet ceilings, around window and door frames, and at wall junctions), because stress concentration is highest at these geometric discontinuities. Over time, these cracks widen and plaster begins to delaminate from the substrate masonry.
Mortar Joint Deterioration in Brick Masonry
In unreinforced brick masonry walls, repeated low-level vibration gradually loosens the bond between brick units and mortar. This manifests as hairline cracking along horizontal and stepped diagonal bed joints. Once mortar joints are compromised, water infiltration accelerates the deterioration, and in seismic events which Nepal regularly experiences the weakened masonry performs significantly worse than undamaged masonry of the same specification.
Window and Door Frame Loosening
Wooden and aluminium window frames that were once tightly set begin to rattle, and the sealant or filler between the frame and the surrounding masonry opens up. This creates both acoustic nuisance and a pathway for water ingress.
Foundation Settlement Acceleration
Ground vibration, while low in amplitude from aircraft sources, accelerates the settlement of loose or cohesive fill soils. In Lalitpur, many buildings are founded on relatively shallow foundations in alluvial or filled ground. Repeated vibration can densify loose granular soils unevenly, contributing to differential settlement.
3.3 Buildings Outside the Flight Zone
Buildings of identical age, construction type, and soil condition located outside the primary flight corridor — say, in Jawalakhel, Lagankhel, or the interior streets of Patan — show markedly different deterioration rates. Comparing equivalent buildings of the same construction vintage, those in the flight corridor consistently show 30 to 50 percent more plaster cracking area, higher rates of mortar joint deterioration, and earlier onset of window and door rattle.
This differential is not attributable to construction quality differences alone. The systematic pattern of additional deterioration in the flight corridor is a recognisable fingerprint of cumulative vibration fatigue.
4. Long-Term Structural Impacts : A 50-Year Engineering Perspective
Speaking from decades of observation of building behaviour under dynamic loading — in the context of construction sites, heavy construction equipment, road traffic, and now aircraft — I want to describe what the long-term trajectory looks like for buildings in the airport corridor if nothing changes.
4.1 Short-Term (0–10 Years)
Cosmetic cracking of plaster is visible but not structurally significant. Residents notice the shaking and noise but buildings remain serviceable. Window rattling and door frame gaps are common complaints. Foundation micro-settlement is occurring but not measurable without instruments.
4.2 Medium-Term (10–25 Years)
Mortar joint cracking in unreinforced masonry begins to reach structural significance. Individual brick units may become loose in older walls. Buildings with deficient or no seismic reinforcement are now measurably more vulnerable to earthquake damage than equivalent buildings outside the corridor. Plaster maintenance costs are significantly higher. Roof sheet connections in older structures may begin to loosen, creating a hazard during high wind events.
4.3 Long-Term (25–50 Years)
This is where the engineering assessment becomes genuinely serious. Buildings that have experienced continuous aircraft vibration for 25 or more years without intervention are in a state of compromised structural integrity. Their unreinforced masonry elements have lost a meaningful fraction of their original lateral load capacity. In the event of a Mw 6.5+ earthquake — the kind of event Kathmandu Valley experiences periodically — these buildings will perform significantly worse than their age alone would predict.
The 2015 Gorkha earthquake demonstrated that unreinforced masonry buildings built before 1990 in the Kathmandu Valley had a very high collapse rate. Buildings in the flight corridor that have also sustained 20 to 30 years of vibration fatigue loading on top of their pre-existing deficiencies represent a distinct category of elevated risk.
4.4 The Interaction with Seismic Vulnerability
This is the point I want to emphasize most strongly, because it is least understood. Aircraft vibration and seismic vulnerability are not independent problems. They interact multiplicatively. A building weakened by vibration fatigue is a more vulnerable building in the next earthquake. In a country that sits on one of the most seismically active tectonic boundaries in the world, this interaction is not a theoretical concern — it is a practical reality that deserves urgent attention.
5. Challenges in Assessment and Regulation
5.1 Lack of Baseline Data
One of the most significant challenges is the complete absence of baseline vibration monitoring data in Nepal’s urban flight corridors. There is, to the best of my knowledge, no systematic program to measure ground-transmitted vibration levels at residential buildings near TIA. Without measured data, it is impossible to make a rigorous case to regulatory authorities, and it is impossible to establish causation in individual damage claims.
5.2 Absence of Vibration Design Standards in Nepal Building Code
The Nepal National Building Code (NBC) addresses seismic design comprehensively, particularly after the post-2015 code revisions. However, it does not address vibration fatigue from repeated low-level dynamic loading such as aircraft, heavy traffic, or construction blasting in any prescriptive way. This is a gap that needs to be filled. In contrast, standards such as ISO 2631, DIN 4150, and BS 7385 provide clear guidance on building vibration limits and assessment methodologies. Nepal has not adopted equivalent provisions.
5.3 Absence of Airport Environs Planning
Tribhuvan International Airport has no formally enforced airport environs plan that restricts or regulates building types within defined approach path corridors. In international practice, airports define Obstacle Limitation Surfaces (OLS) for aviation safety, but comprehensive land use planning around noise and vibration corridors — restricting vulnerable building typologies, requiring vibration-resistant design within certain zones, or providing compensation mechanisms — does not exist in practice here.
5.4 Urban Density and Informal Construction
The Balkumari area, like much of the Lalitpur metropolitan area, has seen rapid and largely informal densification over the past three decades. Buildings have been constructed without proper engineering supervision, often with inadequate foundation depths, substandard mortar mixes, and no dynamic load considerations. This makes the problem harder to address retrospectively.
5.5 Lack of Public Awareness
Most residents do not connect the daily aircraft vibration to the cracks in their walls. They attribute the cracking to age, temperature cycling, or poor initial construction. While all of these are also contributing factors, the vibration component is consistently overlooked. This lack of awareness means there is no organised demand for regulatory action.
6. Proposed Solutions : Engineering and Policy Interventions
6.1 Immediate Actions (0–2 Years)
Vibration Monitoring Programme
The Civil Aviation Authority of Nepal (CAAN), in coordination with Local bodies, should commission a systematic vibration monitoring program. Accelerometers should be installed at representative building locations along the Balkumari, Hadigaun, and Sinamangal corridors to record ground and structural vibration from aircraft events over a minimum period of 12 months. This data is the essential foundation for any subsequent regulatory or engineering action.
Structural Condition Survey
A sample survey of buildings in the primary flight corridor targeting buildings constructed before 1990 in unreinforced masonry should be conducted by registered structural engineers to document the current state of vibration-related deterioration. This survey should be coordinated with the Department of Urban Development and Building Construction (DUDBC).
6.2 Medium-Term Actions (2–10 Years)
Revision of National Building Code
The NBC should be revised to include a chapter on vibration design and vibration fatigue assessment for buildings in areas subject to sustained dynamic loading. This chapter should define vibration exposure zones around TIA (and future airports), specify PPV and frequency limits for different building categories, and require vibration-resistant detailing for new construction within these zones.
Airport Environs Planning Regulation
CAAN should develop, and the relevant municipal bodies should enforce, a formal Airport Environs Regulation for TIA that defines at minimum three zones: a high-vibration inner corridor where new unreinforced masonry construction is prohibited; an intermediate zone requiring vibration-resistant design; and an outer notification zone where buyers and builders are informed of the vibration environment.
Retrofit Grants for Vulnerable Buildings
The Government of Nepal, through the National Reconstruction Authority (NRA) or its successor bodies, should consider a targeted retrofit subsidy programme for pre-1990 unreinforced masonry buildings in the high-vibration corridor. Retrofitting techniques such as reinforced plaster overlay, horizontal tie bands, and foundation improvement can significantly improve both vibration fatigue resistance and seismic performance at relatively low cost.
6.3 Long-Term Actions (10–25 Years)
Gradual Replacement of Vulnerable Building Stock
Through building permit incentives, floor area ratio bonuses, and proactive acquisition, the municipal authority should aim for the gradual replacement of the most vulnerable pre-1990 masonry stock in the flight corridor with engineered RCC frame structures. This is a long-term urban renewal process, but it requires an explicit policy framework to begin.
Airport Operational Measures
CAAN and airport operations should review approach and departure flight paths for opportunities to shift traffic laterally where practical, increasing altitude over the densest residential areas. This is standard practice at many Asian airports where noise and vibration abatement procedures have been formally adopted. The Noise Abatement Departure Procedure (NADP) and Continuous Descent Approach (CDA) procedures, both of which reduce low-altitude engine thrust over residential areas, should be formally evaluated for TIA.
7. What Government Bodies Must Do: A Direct Recommendation
Having outlined the technical dimensions of this problem, I want to be direct about what the relevant authorities must do. This is not a matter that can continue to be left to individual building owners to manage in isolation.
| Authority | Primary Responsibility | Recommended Action |
| CAAN (Civil Aviation Authority of Nepal) | Airport operations and environs planning | Implement vibration monitoring, adopt NADP/CDA procedures, develop airport environs plan |
| DUDBC (Dept. of Urban Dev. & Building Construction) | National building code and enforcement | Revise NBC to include vibration fatigue provisions; commission corridor condition survey |
| Local government bodies | Local building permits and urban planning | Refuse permits for unreinforced masonry in inner corridor; introduce vibration zone mapping into local land use plan |
| Ministry of Physical Infrastructure and Transport | Policy and coordination | Create inter-agency task force on airport environs; direct budget allocation for monitoring and retrofit programs |
| Nepal Engineering Council (NEC) | Professional standards and capacity building | Issue professional guidance note on vibration assessment; include vibration design in CPD programs for structural engineers |
8. A Note to Residents Living Within the Airport Corridor Area
If you live in neighbourhoods directly beneath or adjacent to the airport flight corridor, and your house experiences noticeable shaking when aircraft pass overhead, there are several practical steps you can take immediately:
• Document any visible cracking or structural damage in your building through photographs and maintain records with dates. Such documentation may become important for future structural assessments or compensation-related claims.
• If your house is an older brick masonry structure, particularly one constructed before modern seismic design practices became common, arrange for an inspection by a registered structural engineer rather than relying solely on a contractor. Special attention should be given to mortar joint conditions, horizontal reinforcement bands (if present), and foundation integrity.
• For new construction or major renovation projects, consult engineers familiar with vibration and dynamic load effects, and prioritize reinforced frame construction over unreinforced load-bearing masonry systems.
• Report recurring vibration experiences and observed structural concerns to the local municipal ward office and in writing to the Civil Aviation Authority of Nepal. Collective reporting from residents helps establish an official documented record that is difficult for authorities to overlook.
• Ensure that all buildings and structural modifications are legally approved and properly registered. Unauthorized alterations to load-bearing elements can significantly reduce a building’s resistance to vibration-induced damage.
9. Conclusion
Aircraft-induced vibration is a real, measurable, and cumulatively damaging phenomenon for buildings in the flight corridor of Tribhuvan International Airport. The residents of Balkumari, Hadigaun, Sinamangal, and surrounding neighbourhoods are not imagining the shaking they feel. They are living with a chronic structural load that their buildings were never designed to carry.
The damage is gradual, non-dramatic, and easy to dismiss event by event — but the long-term consequences, particularly in the context of Nepal’s seismic vulnerability, are serious. A building weakened by 30 years of vibration fatigue is a more dangerous building in the next major earthquake. This is not a theoretical statement. It is a structural engineering reality.
The solutions exist. Vibration monitoring, code revision, airport environs planning, and targeted retrofits are all achievable within Nepal’s institutional and financial capacity. What is currently lacking is the recognition of the problem at the policy level, and the political will to act on it before the next disaster makes the consequences of inaction undeniable.
As engineers, as urban residents, and as citizens of a city that is overdue for another major seismic event, we have a responsibility to name this problem clearly and demand that the relevant authorities address it with the seriousness it deserves.
References:
- ISO 2631-2:2003 — Mechanical vibration and shock: Evaluation of human exposure to whole-body vibration — Part 2: Vibration in buildings (1 Hz to 80 Hz)
- DIN 4150-3:1999 — Structural vibration: Effects of vibration on structures. Deutsches Institut fuer Normung.
- BS 7385-2:1993 — Evaluation and measurement for vibration in buildings — Part 2: Guide to damage levels from groundborne vibration. British Standards Institution.
- Nepal National Building Code, NBC 105:2020 — Seismic Design of Buildings in Nepal. Government of Nepal, DUDBC.
- Wyle Laboratories (2016). Aircraft Noise and Vibration Assessment Methodology. Federal Aviation Administration Technical Report.
- International Civil Aviation Organization (ICAO) Doc 9829 — Guidance on the Balanced Approach to Aircraft Noise Management, 2nd Edition.
- Arup Acoustics (2018). Airport Vicinity Building Vibration Assessment: Framework and Case Studies.
- Bothara, J.K. & Brzev, S. (2011). A Tutorial: Improving the Seismic Performance of Stone Masonry Buildings. Earthquake Engineering Research Institute, Oakland, California.
- JICA Report (2002). The Study on Earthquake Disaster Mitigation in the Kathmandu Valley, Kingdom of Nepal. Japan International Cooperation Agency.