Home' Asian Aviation : AAV April 2016 Contents 20 AsianAviation | APRIL 2016
over 10 days following the initial 6.3hr event on
March 9, Airbus tells Asian Aviation.
With the re-engined A320neo family also being
offered with alternative CFM International Leap-1A
powerplants, Pratt & Whitney had been scheduled
to lead flight-testing of the larger A321neo variant,
although in the event trials began with the first Leap-
powered example. Nevertheless, Airbus says the first
delivered A321neo will sport PW1100G-JM units
when it is handed over at the end of the year.
Reporting group results in February, Airbus revealed
that production of Neo models this year would be
“back-loaded” — that is, most examples would be
in the second half of the year, with many “standard”
A320 versions being brought forward to before July.
The move will ease pressure on P&W as it works to
supply upgraded engines for initial A320neos.
Akbar Al Baker, chief executive of Qatar Airways,
insists that he can drop his PW1100G engine
orders as soon as this month [April]: “We are not
waiting indefinitely,” he said in early March. “We
have four aircraft sitting on the ground in Toulouse
with no engines.”
The operator had been scheduled to take delivery
of its first A320neo at the end of last year, before
deferring acceptance because of the engine-starting
issues. But the official explained that, despites his
rights as customer, “we will give P&W a certain
time”; he wanted to ensure that the situation did not
impinge on the growth plans of Qatar Airways, which
has ordered 50 A320neos and A321neos.
Earlier, at February’s Singapore airshow, Al Baker
said he would not take any of the aircraft until the GTF
powerplant was “very much corrected.” Confirming
that Airbus was not at fault, and that he was not
thinking of cancelling any of the Neos, he said: “No
airplane can fly without an engine.” Nevertheless,
Qatar Airways could “cancel the entire [engine]
order” and might have “no alternative” but to switch
to the Leap-1A powerplant.
In response, P&W commercial engines president
Greg Gernhardt confirmed that the manufacturer
had “been working very closely” with the airline: “We
all realize Al Baker is a very demanding customer.”
At the airshow, Gernhardt conceded that there
were “some minor tweaks we have to make” to the
engines, which would be ready for Qatar “in the June
timeframe [when] the engines with all the fixes for the
minor teething issues will be delivered.”
In fact, Gernhardt was echoing pre-airshow
remarks in which he claimed that “minor hardware
and software changes” were all that were needed
to overcome the engine’s operational limits. The
P&W executive was emphatic that the GTF’s “basic
architecture is fine”: P&W did not see any “major”
retrofits or redesigns required. On the basis of
thousands of hours of testing, the manufacturer was
“extremely pleased with the way the aircraft and
engine are performing in service [with Lufthansa].
Fuel burn is spot on.”
As the A320neo was approaching service entry
late last year, it emerged that the PW1100G-JM
powerplant, but not any other GTF variant fitted to
other aircraft, is subject to a phenomenon known
as “rotor bow,” which is the second primary issue
identified by Lufthansa. It is caused by asymmetric
cooling within the engine structure and results in
thermal deformation and slight turbine rotor-shaft
The PW1100G-JM, the A320-specific variant of
the basic PW1000G-JM design, suffers more than
most turbine engines. It is also the only GTF engine
that P&W had to core mount to the pylon (or strut),
all other variants being fan-mounted.
To address the issue, initial operating requirements
specify that the engine be run at “idle” speed (with
the aircraft stationary) for three minutes following
start-up to avoid the risk of minimal bending of the
engine shaft (or “rotor”) under certain conditions.
This is seen by airlines as an inordinately long time
to wait before being able to taxi away from the gate.
(There has also been a software issue that P&W
has addressed via a software fix and update that
increases cooling times between engine runs.)
P&W’s response has been along two lines: first,
all production-standard PW1100G-JM engines now
incorporate a damped bearing, or “damper,” on the
third and fourth rotor-shaft bearings. Typically, in
such arrangements, oil under pressure in the bearing
compensates for slight shaft misalignment and can
absorb shaft vibrations.
“The engines we are building today are to this bill
of material and the first 20 engines we built were not.
With these 20, we have a plan with the customers to
go back and modify them as needed,” according to
P&W president Robert Leduc.
Second, P&W is collecting data from PW1100G-
JMs in service and under accelerated testing, and
to use the information obtained to slowly reduce
overall prescribed engine-start time. By June, Leduc
believes it will be down to 200 seconds and by the
end of this year to 150 seconds.
In one sense, the GTF design might be said to
be a victim of its own success, since its geared
architecture permits the use of higher speeds
using a smaller-diameter shaft that, in turn, is more
susceptible to bowing when subject to differential
heating. (Further, the use of smaller turbine-blade tip
clearances in the eternal search for greater engine
efficiency increases the possibility of blade-scraping
AIRBUS A320NEO FAMILY FLIGHT-TEST TIME
Total block hours
Total flight cycles
A P&W 1100G-JM engine
on the Airbus A320.
AAV_April 2016.indd 20
30/03/2016 6:49:48 PM
Links Archive AAV March 2016 AAV May 2016 Navigation Previous Page Next Page