How One Major Boeing 777 Operator Quickly Tripled Cargo Loads, using RNP-AR


Due to challenging terrain surrounding Kabul, a major international Boeing 777 airline faced regular issues carrying scheduled cargo. Particularly in conditions of low cloud, missed-approach climb gradients were so extreme, cargo was regularly offloaded, costing time and money.

Staff from Xflash Systems developed a new, advanced ‘ILS-to-RNP’ navigation solution to relieve the issue, retaining revenues and increasing efficiency. Here’s how they did it, at a low cost, within 2 months;

Kabul airport is situated in a wide valley, surrounded by mountains with peaks over 11,000ft. The airfield elevation is 5,800ft. This means 777 climb performance is significantly degraded, because air is less dense. Furthermore, lift available from the wing is much less and engines cannot produce thrust available at sea level.

Kabul airport has severe constraints associated with; terrain, Air Traffic Control (ATC), security and direction of turn during all go-arounds. Any pilot approaching Rwy 29 is faced with a “wall” of mountains on the missed approach path from Runway 29.

Without a solution enabling greater cargo carrying capacity, financial and cargo customer service effects to the airline on most Kabul 777 flights would be severe.

Difficult Choices Quickly Lead to a High-Tech Xflash Solution

Staff members at Xflash Systems were tasked to work with members of the airline’s technical staff to develop a new missed-approach navigation procedure for all their 777 aircraft to fly. This enabled the aircraft to carry over three times the previous cargo load, whenever low cloud and/or poor visibility conditions existed.

The existing Kabul Rwy 29 ILS procedure had two published approach minimums, each with a distinct climb gradient; a higher ILS approach minimum of around 1,180ft above ground level (with a less demanding missed-approach climb gradient of 3.3%) and a lower ILS minima of around 320ft (with a much greater climb gradient required of 5.8%).

At Kabul, whenever the cloud ceiling is below 1,200ft the lower ILS minima must be used – together with the associated increase in climb gradient. Unless the 777 aircraft were light enough to achieve a 5.8% climb gradient in an engine-out condition, cargo would have to be offloaded at departure airport (along with an associated financial hit).

While there’s also an RNAV approach to Rwy 29, the RNAV approach has even higher approach minimums than the ILS. The ILS was the best way to get the aircraft to approach minimums in this case.

New Kabul Missed Approach Procedure Developed & Tested Within Weeks

Xflash Systems staff realized early-on during solution development, it was best to continue using the ILS facility and approach to get the aircraft to approximately 600ft above ground. With a new missed-approach design this would allow the aircraft to descend far lower than before, without incurring delays in implementation with ATC and unneeded extra design work. To relieve the stringent climb gradient requirements for missed approach, a new missed approach procedure design was required; one that took advantage of the 777’s superior navigation accuracy; Required Navigation Performance (RNP) 0.11 .

This level of navigational accuracy allowed staff to produce a new missed approach procedure with a much narrower width (20% the width of a conventional missed approach design). Much less terrain either side of track then to be taken into account, allowing a much easier 777 climb gradient of 2.5%, plus certain other climb factors due to the bank angle required during the turning missed approach.

Technical requirements were detailed, along with desired climb gradient and direction of turn. Sophisticated instrument procedure design software was used to analyse terrain towards producing an optimal missed approach track. Once the initial design was ready, it was coded into the Flight Management System (FMS) and readied for testing and evaluation in the airline’s flight simulator.

This simulator evaluation roundly proved the solution Xflash Systems staff members had developed, while confirming the 777 theoretical performance calculations and obstacle clearance. This new Kabul procedure was quickly proven as safe and effective – clearing the critical obstacle (a ridge to the north of the airport) by the expected margin.

Summary & How Your Organization Can Benefit

This detailed process and new Kabul ILS-to-RNP design allow this major international 777 operator to carry significantly more cargo into Kabul, while meeting all safety and regulatory requirements. The airline’s investment in pilot training and 777 equipment have further enabled the operator to extract value from their regulatory approvals to conduct RNP–AR (Authorisation Required) instrument approach procedures.

The operator is now reaping the financial benefits of their investment in people, procedure designs and RNP-AR technology.

The development process followed by Xflash Systems demonstrates how maximum benefit may be extracted by airlines, governments and business jet operators, to take advantage of today’s advanced aviation navigation technology, procedure design systems and Xflash Systems knowledge.

The operator concerned is now increasing cargo revenues to Kabul through their significant reduction in 777 climb gradients, leading to; lower costs, greater assurance of delivery and more efficient operations all-round.

If you would like to carry more cargo, develop new instrument procedures, achieve greater efficiencies and generally squeeze more money out of your flight operations, please contact Xflash Systems HERE or email us; and see how we can help you.

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