Great-circle distance is the shortest path between two points on the Earth's surface: the route an aircraft would fly if there were no airways, winds or closed airspace in the way. On a flat map it appears as a curve, but on a globe it is the most direct line between the two points, and it is the standard way of measuring how far apart two airports are. It says rather less about how long the flight will take, what it costs to overfly the states in between, or what the sector costs to operate. On the Istanbul–Delhi route, with Iranian, Pakistani and Chinese airspace excluded, those gaps produce what might be viewed as a counter-intuitive result: the longer routing carries lower navigation charges, yet a materially higher break-even fare.
Key findings
- Avoiding Iranian, Pakistani and Chinese airspace adds around 1,340 km (29%) to the sector, taking the flown distance from 4,556 km to 5,896 km.
- En-route navigation charges fall by USD 348 per sector (12%), from USD 2,826 to USD 2,478, because the southern routing avoids a long distance in Turkish airspace and Afghanistan's USD 700 overflight charge.
- Block time rises by 80 minutes (21%), from 390 to 470 minutes.
- The breakeven fare rises by 16%, from USD 180 to USD 209 per passenger, requiring around USD 4.15 million a year in additional revenue on one daily return service.
- The navigation saving is worth about USD 1.74 per passenger, against a net cost increase of USD 28.47. Flying time and fuel burn, rather than overflight charges, determine the economics of the detour.
Table 1: At a Glance - Indio A321neo, 90% Load Factor
The direct routing: shorter, but more expensive to overfly
Without airspace restrictions, the shortest path from Istanbul (IST) to Delhi (DEL) runs north of the Gulf, across Turkey, Iran, Afghanistan and Pakistan into India. The flown and chargeable distance is 4,555 km, and en-route navigation charges total USD 2,826 for the sector (Figure 1). Two states account for most of that bill. Turkey (USD 842) and Afghanistan (USD 700) together make up almost 55% of the total cost. The balance is spread across Iran (USD 293), Pakistan (USD 293), Turkmenistan (USD 259), Azerbaijan (USD 236), India (USD 159) and Armenia (USD 44).
Figure 1: Direct routing with no airspace restrictions applied. Source: RDC Aviation En-Route
The avoidance routing: further to fly, cheaper to overfly
With Iranian, Pakistani and Chinese airspace excluded, the routing changes entirely (Figure 2). It heads south across Cyprus and Egypt, tracks along Saudi Arabia, Bahrain and the UAE, and crosses Oman before entering India clear of Pakistani airspace. The flown distance is 5,896 km across six waypoints: roughly 1,340 km, or 29%, further than the direct routing. En-route charges on this longer sector total USD 2,478 across eight states. Saudi Arabia is the largest single item at USD 687, followed by Turkey (USD 392, much reduced because the routing crosses a shorter Turkish segment), Oman (USD 326), Cyprus (USD 323), India (USD 293), the UAE (USD 217), Bahrain (USD 124) and Egypt (USD 115).
Figure 2: Istanbul–Delhi with Iranian, Pakistani and Chinese airspace excluded. The routing (blue) runs south via Turkey, Cyprus, Egypt, Saudi Arabia, Bahrain, the UAE, Oman and India; excluded airspace is shown in red
Block time: where the extra distance is really paid for
The picture changes once the operating economics are modelled. The scenario assumes one daily return service with a 222-seat IndiGo A321neo at a 90% load factor, equivalent to around 145,900 passengers a year. The direct routing schedules at 390 minutes block time and the avoidance routing at 470 minutes: 80 minutes, or roughly 21%, longer (Figures 3 and 4). Costs are shown per passenger and split into direct operating costs (DOC) and indirect operating costs.
Figure 3: Direct routing: 390 minutes block time, USD 180.48 breakeven fare, itemised costs
Figure 4: Avoidance routing: 470 minutes block time, USD 208.95 breakeven fare, itemised costs. Source: RDC Aviation Apex Route Performance
Fixed (standing) DOC covers the ownership, depreciation and insurance costs that accrue with flying time. It rises from USD 29 to USD 35 per passenger (+21%), almost exactly in line with the 20.5% increase in block time.
Variable DOC covers fuel, maintenance and navigation charges. It rises by a more modest 15%, from USD 132 to USD 152. The lower en-route charges on the avoidance routing offset only a small part of the additional fuel burn and time-driven maintenance.
Indirect operating costs move least, rising 12.5% from USD 19 to USD 22, as they are only loosely linked to block time.
Total costs, which equal the breakeven fare, rise 16%, from USD 180 to USD 209 per passenger. Over a year, the avoidance routing must generate around USD 4.15 million in additional revenue simply to break even.
Table 2: Itemised Cost Lines, per Passenger
Two costs pulling in opposite directions
Taken together, the two analyses do not support a simple conclusion that avoidance costs more. On en-route charges alone, the detour is the cheaper option. The additional 80 minutes of block time, however, brings extra fuel burn, higher crew and ownership costs and fewer rotations from the same aircraft, and raises the break-even fare by almost 16% regardless of the navigation bill. The two effects move in opposite directions, and neither is visible from distance and load factor alone.
For airlines and lessors assessing corridors that cross politically sensitive airspace, the lesson is to model the routing end to end. A route that looks marginal on distance may carry a lower navigation bill than expected; an apparent shortcut may carry an overflight charge, or a schedule penalty, that only emerges once the routing is modelled in full.
Frequently asked questions
Why is the longer routing cheaper in navigation charges? Overflight charges depend on each state's rates and flat fees, not on distance alone. The direct routing incurs a long Turkish segment (USD 842.13) and Afghanistan's USD 700.00 charge; the southern routing spreads its charges across a series of smaller Gulf-state fees.
Why does the breakeven fare still rise? The avoidance routing adds 80 minutes of block time, which drives up fuel, maintenance, crew and ownership costs. Per passenger, these outweigh the navigation saving many times over.
How much additional revenue does the avoidance routing need? Around USD 28.47 more per passenger, or roughly USD 4.15 million a year on one daily return A321neo service at a 90% load factor.
Scenario and assumptions
- City pair: Istanbul (IST) to Delhi (DEL)
- Aircraft: IndiGo A321neo, 222 seats
- Frequency: one daily return service
- Load factor: 90%, equivalent to around 145,900 passengers a year
- Airspace excluded in the avoidance case: Iran, Pakistan and China
- Currency: all figures in US dollars (USD); costs are per passenger unless stated
- Data: routings and en-route charges from RDC Aviation's En-Route module; block times and operating costs from RDC Aviation's Apex Route Performance module
Notes
The Istanbul–Delhi scenario is illustrative and does not reflect IndiGo's current operation on the route.
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