British Airways flight BA 38 accident and Jet A-1 fuel temperature - part 4
British Airways flight BA 38 accident and Jet A-1 fuel temperature - part 4
This
is in continuation of “British Airways flight BA 038 flight altitude and Cold fuel Management - part 3”, a blog series for understanding Aviation
turbine fuel’s role in modern civil flights specially behavior of water
in fuel to mitigate it’s adverse effects during flight, including at
high altitude where water will turn into ice.
The
article and next parts covers fuel temperature at various stages
during flight journey, from Beijing refuelling to London after crash remaining
fuel in aircraft tanks, and gives insight of fuel temperature measuring and
controlling systems for avoiding ice adverse impacts.
Sr.
No.
|
Place, flight state, time
|
Jet
A-1 Fuel Temperature
|
Remarks
|
1
|
Beijing,
Flight arrival 0009 hrs on 17
January 2008, before refuelling, aircraft product,
|
-20°C
|
Arrival
fuel Quantity
8100 kg
|
2
|
Beijing Aircraft refuel temperature. Flight departure commenced 0155 hrs on 17 Jan 2008
|
5°C,
|
Jet
A-1 Refuel quantity
71,401
kg
ambient
temperature (-7°C)
|
3
|
At the time of Engine starting for take off. Aircraft
took off at 0209 hrs
|
-2°C
|
28,900
kg in each of the main fuel tanks and 21,200 kg in the centre fuel tank
|
4
|
The aircraft altitude of 10,590 m (34,750 ft),
where, at 0232 hrs, it levelled off into the cruise portion of the flight
|
-2°C
|
|
5
|
At 0436 hrs, about two hours into the cruise, the
left main tank fuel temperature had progressively reduced to about -22°C.
|
-22°C
|
|
6
|
During the next three and a half hours, fuel
temperature reduced further from -22°C to -32°C
|
-32°C
|
|
7
|
At 0930 hrs, fuel temperature reduced to its lowest
recorded value of -34°C. It remained
there for about 80 minutes
|
-34°C
|
|
8
|
At 1202 hrs the aircraft started its descent. The aircraft levelled at FL110
|
-22°C
|
|
9
|
Fuel temperature at the time of the fuel reduction
to both engines 1208 hrs during Approach
|
-22°C
|
|
10
|
After the accident fuel was seen to leak out of the
ruptured engine fuel pipes until the spar valves were closed.
|
-
|
Estimated
fuel leak was approximately 6,750 kg
There
was no fire.
|
11
|
Following
the accident, 66 fuel samples were taken from the aircraft, and engines. The first fuel samples were taken within two hours of the accident from the fuel leaking out of the fractured engine fuel pipes. Samples from the engine fuel filters and the right main tank sump drain were taken the following day |
-
|
The
fuel samples from G‑YMMM
complied fully with the specifications for Jet A-1. The sampled fuel had a fuel freeze
temperature of -57°C and water content of between 35 and 40 parts per million
(ppm).
The
samples were clear of any microbial growth and did not contain any anti-icing
additives such as Fuel System Icing Inhibitor (FSII)
|
12
|
Beijing ambient temperature
|
-
|
-7°C
|
13
|
initial cruise altitude of FL348
|
-
|
Air
temp estimated -65°C
|
14
|
After crossing the Ural mountains, the aircraft
climbed to FL380. At that time the area between the Urals and Eastern
Scandinavia, there was a region of particularly cold upper winds, with
temperatures en route as low as -74˚C.
|
-
|
Air
temperature further dropped to -74°C
|
15
|
Heathrow weather, arrival ATIS at 1240 hrs on 17
January 2008
|
-
|
The
surface temperature was +10°C
|
Fuel temperature measurement
The fuel temperature indication system has a temperature
probe located between ribs 9 and 10 in the left main tank. The probe is situated approximately 12.6
inches above the lower wing skin and is located 40 inches outboard of the aft
boost pump inlet. The fuel in the left
wing tank can be slightly colder than the right wing tank. This is because the right fuel tank contains
two hydraulic fluid/fuel heat exchangers, which are used to cool the hydraulic
fluid, whereas the left wing has only one.
Max and minimum Fuel Temperature :
Boeing 777 has operational limitation of Jet A-1 fuel temperature as max 49°C and min 3°C above the freezing point. In absence of actual freezing point limit is -44°C. ( specification -47+3°C).In case of Low fuel temperature :
Operational guidelines in condition of Fuel temperature approaching to minimum limit- Increase airspeed, change altitude, and/or deviate to a warmer air mass to achieve a TAT equal to or higher than the fuel temperature limit (3 degrees C above the fuel freeze point). TAT increases approximately 0.5 to 0.7 degrees C for each 0.01 increase in airspeed. In extreme conditions it may be necessary to descend as low as FL 250.
Fuel temperature is displayed in white on the
primary Engine Indicating and Crew Alerting
System (EICAS).
The EICAS low temperature warning trigger automatically defaults to the
freezing limit of Jet A,
unless another temperature, such as the freezing point of Jet A-1, has been set
in the Flight Management Computer (FMC) Control Display Unit (CDU). Once the fuel temperature reaches 3°C above
the fuel freezing temperature (-37°C for Jet A and -44°C for Jet A-1) the fuel
temperature indication turns amber and the fuel temp low advisory message is
displayed on the EICAS.
Flight Data Recorder (DFDR) – Fuel Temperature recording
In accordance with regulatory requirements, the aircraft was
equipped with a 25-hour duration DFDR and a 120 minute Cockpit Voice Recorder (CVR).
Fuel temperature within the left main fuel tank (recorded by
the DFDR at a rate of once every 64 seconds and by the QAR at a rate of once
every four seconds). Temperature was
recorded by both DFDR and QAR to a resolution of 1°C.
On long flights the temperature of the fuel in the main wing
tanks will tend towards the temperature of the boundary layer around the wing,
which can be up to 3°C lower than Total Air Temperature (TAT). Whilst the cheek tanks of the centre tank are
situated in the wings, and are affected by aerodynamic cooling, the majority of
the centre tank fuel is sandwiched between the cabin and the air
conditioning packs. Consequently the
fuel in the centre tank is considerably warmer than the fuel in the main tanks.
In this part, we have seen fuel temperature at various stages
of flight, how it is measured and recorded. How it is displayed in DFDR and
compared against freezing point of fuel to alert crew for any deviation
.
In next part, we will see fuel system on the board for idea
on fuel storage, pumping, sumping, filters, fuel heat exchangers etc.
-B777 flight manual
- Wikipedia https://en.wikipedia.org/wiki/British_Airways_Flight_38
Author's Profile
List of all blog articles on Petroleum QC by RJ Patel.
References:
Report on the accident to Boeing 777-236ER, G-YMMM, at London Heathrow Airport on 17 January 2008
List of all blog articles on Petroleum QC by RJ Patel.
References:
Report on the accident to Boeing 777-236ER, G-YMMM, at London Heathrow Airport on 17 January 2008
-B777 flight manual
- Wikipedia https://en.wikipedia.org/wiki/British_Airways_Flight_38
Earlier parts of this series
Comments