Explainer: Why enforcing height restrictions around aerodromes is critical for flight safety

The gazette notification of the draft comes about a week after the crash of an Air India Boeing 787 long haul aircraft at Ahmedabad a few seconds after it got airborne, killing 141 passengers and crew members on board besides killing and injuring dozens of persons on the ground and damaging several buildings. The rules are among the efforts aimed at preventing future accidents because of flight path obstructions.

What are the hazards posed by buildings

Buildings, structures like water tanks or transmission towers and tall trees around airports can interfere with aircraft operations and pose potential hazards to flight safety as well as the security of the installations.

According to aviation experts, structures in the flight path may require pilots to deviate from the ideal rate of descent or ascent. This creates additional risk during low visibility conditions such as fog or low clouds.

Permanent concrete structures in the runway’s funnel can also affect the surface temperature and wind shear and create drafts, requiring different power settings and glide path angles during approach or take-off.

Trees and houses along the aerodromes’ perimeter also attract birds, which are a major hazard. A bird hit during the critical phase of landing or take-off, especially if injected by an engine may result in a ‘flame-out’, i.e. the affected engine switching-off, which may lead to a catastrophe.

Then there are other related issues like radio signal transmissions that may interfere with an aircraft’s navigation and communication systems as well as physical security as tall structures give a line-of-sight visual access to sensitive areas inside an aerodrome.

Most Indian airports face the problem of heavy construction around their peripheries, despite regulations to the contrary. There are instances where houses or sheds abutt the aerodrome’s perimeter wall and in some cases have even blocked the emergency access to the runway from outside.

What are the height restrictions around aerodromes

The Directorate General of Civil Aviation (DGCA) and the Airports Authority of India (AAI) have specified the permissible height of structures that can be built in the vicinity of aerodromes or along the flight path to and from the runway.

The restrictions on height are different in the runway’s funnel, that is the specified triangular area beyond the either end of the runway that defines the flight path of aircraft landing and taking off, and different for other areas around the perimeter, where higher structures are permitted.

The height restrictions in the funnel are guided by the angle of descent or angle of ascent of an aircraft mandated for safe and smooth operations. This is the most critical area of enforcing restrictions and extends several kilometers beyond the runway’s edge. These also vary according to the size or the category of an airport and the type of aircraft expected to operate from a particular aerodrome.

A No Objection Certificate (NoC) is required to be obtained from the AAI for any construction within the notified areas. The intended use of the structure, environmental factors, safety margins and security perception are factors considered for grant of NOC. The district administration is responsible for the enforcement of safety rules outside the aerodrome perimeter.

What are the new rules?

The new rules state the officer-in-charge of an aerodrome may serve a notice to the owner or user of owners of buildings, structures or trees viewed as violating the prescribed height limits. Owners must submit detailed information, including structure dimensions and site plans, within 60 days.

If the Director General of Civil Aviation (DGCA) or an authorised officer confirms a violation, they may issue an order directing the owner to demolish the structure or cut the tree or reduce their height as directed, within 60 days. Another 60-day extension may be granted only on specific grounds.

The failure to comply could result in enforcement action, including demolition or height reduction. Officers have been empowered to enter the premises during daylight hours for physical verification after informing the owner, and in case of non-cooperation, they may proceed based on available information and refer the matter to the DGCA.

The rules also give owners the right to appeal orders to the First or Second Appellate Officer. However, only those who comply with the orders may claim compensation under Section 22 of the Bharatiya Vayuyan Adhiniyam, 2024.

Why are the rules important?

Growing pressure on land for housing and commercial purposes has shrunk the safety corridors around aerodromes. Besides approved projects, there has also been heavy encroachment and illegal constructions near airfields across the country and the new rules define a clear, step-by-step administrative and legal process to address the issue.