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Delhi International Airport Limited (DIAL), which operates India's largest airport, dismissed the expert committee report as "inaccurate", claiming it relied on "probabilities, hypothesis, and conjectures" rather than empirical data or complete documentation.
A flawed design, inferior workmanship, inadequate maintenance, and major discrepancies between design and construction were possible key factors in the collapse of the canopy at Terminal 1 of the Delhi Airport on June 28 last year amid heavy rain, according to the report submitted by the expert committee appointed by the Directorate General of Civil Aviation (DGCA).
The collapse had killed a 45-year old cab driver, Ramesh Kumar, and had injured at least eight others.
Delhi International Airport Limited (DIAL), which operates India's largest airport, dismissed the report as "inaccurate", claiming it relied on "probabilities, hypothesis, and conjectures" rather than empirical data or complete documentation.
However, the operator said it had not provided all documents to the committee during the investigation.
DIAL attributed the roof collapse solely to incessant rainfall -- the highest in the region since 1936 -- which led to water accumulation exceeding the structure's load-bearing capacity, stating it was beyond their control.
A three-member panel of Indian Institute of Technology (IIT) Delhi and IIT Jammu civil engineering professors -- Dipti Ranjan Sahoo, K N Jha, and Deepak Yadav -- submitted its report on October 1, 2024.
Two weeks later, the Airports Authority of India (AAI) issued a show-cause notice to DIAL, citing a "grave and inescapable lapse" on the operator's part.
DIAL responded on December 10, 2024, followed by further clarifications earlier this month -- on February 4, 2025.
The AAI, which works under the ministry of civil aviation, is yet to take a final decision on this matter, according to sources.
Business Standard has reviewed multiple documents related to this matter. The DGCA, IIT Delhi, and the ministry of civil aviation did not respond to queries sent by the newspaper.
Primary cause
The expert panel identified a critical design flaw: the horizontal beam was assumed to be at the top of the flared columns but was actually attached midway, altering the force distribution and stressing the weld joints.
Moreover, the actual welding penetration was "most likely" 40 mm instead of the required "full-depth" 60 mm, weakening structural integrity.
The committee analysed 12 different scenarios and found that in many cases, the stress on the structure reached its "yield point," the maximum stress before permanent deformation.
"From the above analysis, it can be concluded that the collapse of the roof was primarily due to the failure of the weld in the fin connection (joint) of the horizontal tie member (beam) of a column. Most of the welds were not properly executed as can be seen in the failure photographs (taken from the collapse site)," it stated.
Heavy rain and water accumulation further increased the load, accelerating failure, it added.
However, in its December 12 response, DIAL dismissed these findings, arguing that the panel incorrectly assumed that lower grade Fe 410 steel was used in these structures, welding was done on-site, and weld penetration was just 40 mm.
Instead, DIAL claimed that higher grade Fe 490 steel was used and welding was done in a dedicated shop, and therefore, the structure had higher yield stress (350 MPa vs. 240 MPa).
The operator asserted that the committee's conclusions were unreliable as they were based on visual observations rather than test reports.
DIAL also rejected claims of waterlogging affecting the load, citing compliance with the National Building Code and regular pre-monsoon maintenance.
Photos from cleaning done during April-June 2024 period were provided as evidence.
Missing documents
The panel used Fe 410 steel in its calculations because DIAL failed to provide complete design drawings.
Over two months after the report's submission, DIAL admitted to the AAI that critical documents, including certain updated design revisions done between 2007 and 2009, were not "available" for the committee when it was doing its investigation.
DIAL later retrieved documents showing Fe 490 steel was used, arguing that the committee's conclusions were flawed due to incomplete information.
DIAL attributed the missing documents to the age of the construction project, stating that some records from 15 years ago were not "readily traceable".
In its report, the committee also cited untraceable or unavailable records, such as structural analysis models made using "STAAD or ETABS" software applications, and calculations for the Response Reduction Factor (R-value) that are essential in earthquake-resistant design.
The lack of these records raised concerns about whether key safety factors were considered.
Responding to a Business Standard query on the missing STAAD model, a DIAL spokesperson said that over 100 drawings and design reports were provided to the committee for review.
The claim that the STAAD models were missing is "incorrect", the spokesperson added.
Faulty design
The committee found that the "live load" -- temporary or moving weight a roof must support -- for the curved roof was underestimated at 0.5 kPa instead of the Bureau of Indian Standards (BIS) requirement of 0.75 kPa.
Additionally, the BIS mandates rainwater accumulation must be considered, but the design omitted this critical load factor, potentially underestimating stress on the structure.
DIAL disputed this claim, stating that BIS allows live load reduction for curved roofs.
It asserted that even at 0.75 kPa, the structure remained safe within stress limits.
Inferior workmanship
The panel found other significant discrepancies between design drawings and actual construction.
Purlins (roof-supporting beams) were supposed to rest directly on the top bar of the truss but were instead supported by two thin welded plates.
These modifications were neither updated in the "as-built" drawings nor validated through structural analysis, it found.
Other concerns included poor fabrication, misaligned purlin joints at high-stress points, and improper false ceiling installation.
The fin plate, crucial for structural stability, was not fully welded as per design specifications, weakening connections.
Some truss parts lacked "stiffening" reinforcements, causing them to buckle under stress.
In its observation, the committee said it found "inferior workmanship in fabrication and execution, particularly welded connections".
It stated that the detailing and design of connections, particularly welded connections, were not carried out adequately.
"In the absence of any documents, it appears that this important aspect was left to the fabricators for their own interpretation/execution," it added.
When Business Standard asked about these findings, DIAL said that the design and welding were executed by a specialist steel agency, Geodesic Techniques, which holds ISO 9001 certification.
DIAL also pointed out that a NABL-accredited laboratory tests showed weld quality was satisfactory, contradicting the expert panel's findings.
Maintenance lapses
The committee noted rusted welds in failure photographs, suggesting inadequate periodic maintenance.
While DIAL claimed pre-monsoon maintenance was conducted, the committee said fireproof paint and anti-corrosion measures were missing in the collapsed portion.
DIAL countered that the rust seen was likely just "superficial" surface oxidation and cited tests from a NABL-accredited lab that found no material weakening.
It also argued that fire protection coatings were not required as per the norms of the National Building Code and National Fire Protection Association.
AAI Show Cause and DIAL response
The AAI's October 15 show-cause notice held DIAL accountable for a "clear and inescapable lapse of a grave and compelling nature", stating that the collapse demonstrated "beyond the shadow of doubt" the operator's failure to comply with its Operation, Management, and Development Agreement (OMDA).
The notice warned of action against DIAL's leadership.
DIAL, in its December 12 response, rejected the notice as "unwarranted and incorrect," arguing that the expert panel never explicitly concluded an "inescapable lapse."
It further stated that its senior management could not be held liable under OMDA's provisions.
The ball is in the AAI's court now.
Feature Presentation: Aslam Hunani/Rediff.com
