(In para 13, corrects to show that Boeing already publishes its backlog at net discounted value, not at list-price value.)
* Airbus to disclose net discounted value of backlog at end-year
* Says IFRS15 accounting rule change will reflect minimum revenues
* Jetmaker had been expected to shed light on discounts at Q1
* Airbus, Boeing said to sell jets for around half the list price
By Tim Hepher
PARIS, April 27 (Reuters) - It's one of the worst-kept secrets in aviation, but Airbus kept investors waiting a little longer on Friday for confirmation that it sells planes at huge discounts to official prices.
The European company switched accounting standards for its first quarter results and said in February this would include unveiling the value of its huge order book. But the figures were absent in its results on Friday.
"We will disclose the full backlog in value at the latest in our 2018 results," a spokesman explained, adding this would reflect "minimum future revenues".
The plan to shed some light on actual pricing created a buzz in an industry where manufacturers have long insisted airlines keep individually negotiated prices secret.
Traders and bankers say an aircraft typically sells for no more than half the list price.
Airbus' arch-rival Boeing offers similar discounts, they said.
The practice is something of an oddity in any industry with few suppliers, excess demand and high barriers to entry.
But the discounts also reflect a winner-takes-all mentality in which a plane deal does not just bring short-term rewards, but opens the door to lucrative relationships that can last decades.
These are hard for rivals to break without offering lowball prices, buying back a competitor's planes or giving away expensive perks like retraining pilots.
"The mystery of the duopoly between Airbus and Boeing is that despite everything there is incredible competition," a senior industry executive said.
At the end of 2017, Airbus had 997 billion euros ($1.21 trillion) of planes waiting to be produced, based on catalogue prices.
Sources close to both companies said the airlines understand the value of their jets, and that within their marketplace there is no significant pressure on prices of their key models.
Boeing already reports its backlog at net discounted prices, with unfilled commercial orders worth $415 billion at the end of the first quarter. But it recently trimmed the size in units of its backlog to reflect planes unlikely to be delivered - also following new accounting rules.
Neither firm is expected to lift the secrecy over individual deals, meaning air shows will continue to generate headlines based on artificially high prices.
List prices are not without a purpose, however.
They are used to calculate "escalation" clauses by which planemakers regularly claw back part of the price concessions to compensate for inflation during long production waiting times.
Because some rush to buy with cheap loans or shaky business plans, a few inevitably ask to delay delivery and this is where manufacturers enjoy a "pay day" by adding on escalation, Aengus Kelly, head of leasing firm AerCap, said in a recent interview. ($1 = 0.8264 euros) (Reporting by Tim Hepher; Editing by Elaine Hardcastle/Adrian Croft)