In my previous article I highlighted the faulty glideslope at Bengaluru International Airport (BIA) being a contributor to delays, especially in times of fog. Last Sunday January 24, 2009, BIA, again, experienced significant delays due to fog.

This issue has been hanging fire at Bengaluru International Airport since opening day.

I came across an article by Capt. A. Ranganathan, an Airline Instructor Pilot on Boeing 737 with a flying experience of 20,000 hrs, which explains the situation more technically, and with the right dose of humour.

To err is human but when an error is committed repeatedly, one must credit them with complete incompetence. They have proved that they are champions in “Bending it like Beckham”!

New Greenfield airports are constructed in Bangalore and Hyderabad. The runways are located in areas free of obstacles and the builders install PAPIs (Precision Approach Path Indicators) at a perfect 3° angle. PAPIs are mandatory equipment required by ICAO for airfields where airliner jets operate. These assist pilots to complete a precise landing in the touch down zone after they transition from an instrument approach. All the four runways, two in each city, had these installed at 3° angle.

The AAI installed the ILS (Instrument Landing System) for all the four runways. And they showed why they are great fans of the footballer. They bent the glide slope angles to 3.30° and 3.40°, instead of synchronising them with the 3° PAPIs. With this master-stroke, they killed the two airports from being capable of operating flights in CAT 2 and CAT 3 ILS conditions in fog. The recent diversions from Bangalore and Hyderabad, and the resultant air traffic congestion at Mumbai could have been avoided if the ILS Glide Slope had been less than 3.25° . The airport owners should have insisted on the AAI redoing the glide slopes. Instead, they bend the PAPI angles up to synchronise with the ILS! This is progressive thinking! Airports which should have functioned ‘24 x 365’ hours in a year are restricted to operations ONLY when the visibility is more than 550 metres,

High Glide Slope angles at Hyderabad and Bangalore. Photos: Naverus and Capt. A. Ranganathan

The implications do not stop there. All aircraft have a structural limit for their landing gear. The maximum rate of descent permitted is 600 feet per minute. A glide slope up to 3.25° will ensure a controlled flare and landing within this limit. Any higher angle will require a descent rate of 800 to 900FPM. A positive flare in the correct time is required. Any delay can result in a hard landing or a late touch down. These are a major threat while landing in heavy rain conditions. If the rain condition is accompanied by changing winds, especially tail winds, it becomes a dangerous recipe.

Read the full article here.

Monday June 16 2008

Monica Jha

BANGALORE: Pilots from two airlines (one domestic and one international) have reportedly complained about problems in landing using instrument landing system (ILS) at the Bengaluru International Airport.

The runway (27 orientation, which is being used presently) at the new airport has a 3.4 degree glideslope for an ILS approach while the international standard for the same is 3 degree. The 3 degree glideslope (the angle of descend with respect to horizontal plane) is an acceptable descent profile world over and, therefore, auto pilots are designed for this profile. At BIA, which has a glideslope of more than 3 degrees, auto pilots do not work and pilots need to resort to manual landing, that can cause hard landing at times.

A three-degree glideslope gives a descent of approximately 318 feet per nautical mile (NM) while for a 3.4-degree glideslope, the descent would be about 370 feet per mile which means an aircraft would descend at a higher speed than recommended.

When an aircraft on ILS follows a 3 degree glideslope, passengers do not feel any discomfort but a 3.4 degree glideslope may result in a steep landing causing discomfort to passengers. The operator of BIA, Bangalore International Airport Limited (BIAL), apparently made a mistake in assessing the elevation of glide path location.

On a continuous descent, an aircraft must maintain a height of 50 feet at the threshold of a runway. Due to errors in calculating the elevation this height at BIA was found to be less than 50 feet. So, BIA had to increase the glideslope to maintain a height of 50 feet at the threshold of runway. However, the glideslope for runway when used in 09 orientation is 3 degrees.

To ratify the problem, BIA would need to relocate its glide path antenna further up, an expert from the aviation industry told this website's newspaper. "But, changing the position of glide path antenna at a live airport and a live runway is not possible as landing without ILS for a few days that would be necessitated for calibrations, would be extremely difficult. BIAL can do it when they change from 27 to 09 runway in November," he added.

Source : The New Indian Express