Inflight Fire

 Inflight Fire

Captain Shem Malmquist

·        June 2, 1983, Air Canada flight 797 experienced an in-flight fire.  The first hint of smoke odor occurred at 1900 CDT.  The crew had thought they had extinguished the fire.  At 1907 CDT the smell of smoke returned, and just two minutes later aircraft electrical systems began to fail.  The flight crew was able to get the aircraft on the ground, landing just 13 minutes later.  90 seconds later the fire flashed over, killing 23 passengers. 

·        February 7, 2006, a UPS DC-8 crew detected a faint odor that smelled like burning wood as they descended from FL330  enroute to Philadelphia.  25 minutes later they touched down on 27R at PHL.  The crew stopped the aircraft and the cockpit filled with smoke.  The crew evacuated and the aircraft subsequently became engulfed in flames.   

·        September 5, 1996, a FedEx DC-10 crew responded to  in-flight smoke.  Landing just 18 minutes later in Newburgh, New York, the crew and jumpseaters evacuated the aircraft.  The aircraft was destroyed by fire.  

·        September 2, 1998, just barely over two years later, a Swissair MD-11 crashed less than 21 minutes after the pilots first noticed an unusual odor in the cockpit.   

·        September 3, 2010, a UPS 747-400 crashed while attempting to land in Dubai, UAE.   The flight was approximately 120 miles west of Dubai when the crew first declared an emergency.

As with any other emergency, surviving an in-flight fire requires sound procedures and regular training to ensure we, the flight crew, follows those procedures.  Unfortunately, a fire is one emergency that can kill you even if you do everything right, as the resources traditionally available to us have significant limitations.  Consider, for example, the procedures to depressurize the aircraft, a standard part of the checklist for cargo aircraft.  FAA tested this procedure and found that:

… test results showed a reduced burn rate for all materials tested as the altitude increased (pressure decreased). The decreased burn rate was nearly linear, slightly greater than a reduced rate of 2% per 1000 feet. Testing of lithium metal and lithium ion batteries, a fire safety area of concern for all transportation modes, showed that altitude had little or no effect on the reaction. However, the time needed to heat the batteries to the point of reaction was increased, because of the reduced burn rate of the fuel supplying the heat, as altitude was increased (pressure reduced).

… test results showed that although depressurization reduced the initial burning, the fire intensity on decent was greatly accelerated. The highest depressurization altitude evaluated (25,000 feet) produced the best initial results but the largest fire on decent.[i]

These findings should not be construed to mean that we should not depressurize.  Absent a better solution, depressurization provides one of the best known methods to buy us time.  Time is what we need to get on the ground.  Knowledge of the research, however, might provide some clues as to how and when you might want to plan your descent in the event of a fire.

One company, FedEx, has been very proactive in providing measures to protect their crews.  The company has installed full-face oxygen masks, and the standard oxygen supplies on FedEx aircraft are well above the regulatory requirements.   FedEx has designed, developed and certificated a cargo fire suppression system as well as fire suppression (“Peltz”) pallet bags.  These are being installed on long range aircraft.  The Peltz material has been tested to contain a fire for up to four hours.  Those cargo containers with plexiglass are being modified to all aluminum, and Peltz bag material is replacing the plastic sheeting in the containers.  All of these measures will increase the time crews have to get the aircraft on the ground.   Other companies are now implementing similar measures.

Are you prepared should you encounter a fire?

There are things that we, as pilots, can do that will significantly improve our odds of surviving an in-flight fire.  The first thing to remember is that it is vital that you follow your training as closely as possible.  It is vital that you become familiar and follow the checklists in your aircraft as closely as possible.  A real fire is not the time to be fumbling with the checklist due to unfamiliarity, however, that does not mean that we can learn things to make the most of our procedures, such as the lesson above from the FAA studies of the effects of depressurization on fire.

Reading through the list of brief synopsis above, a common theme is how little time we have to respond to an in-flight fire.  A Canadian Transport Safety Board study found that your chances of surviving an in-flight fire decrease significantly after about 20 minutes, dropping to a very low probability after 35 minutes.

The following chart depicts the time that various crews had from the first indication of the presence of a hidden fire, to the time that fire became catastrophically uncontrollable[ii]:

DATE	LOCATION	AIRCRAFT TYPE	TIME TO BECOME NON-SURVIVABLE (MINUTES)
07-26-1969	BISKRA, ALGERIA	CARAVELLE	26
07-11-1973	PARIS, FRANCE	B-707	7
11-03-1973	BOSTON, USA	B-707	35
11-26-1979	JEDDAH, SAUDIA ARABIA	B-707	17
06-02-1983	CINCINATTI, USA	DC-9	19
11-28-1987	MAURITIUS, INDIAN OCEAN	B-747	19
09-02-1998	NOVA SCOTIA, CANADA	MD-11	16

A fire onboard an aircraft creates numerous hazards.  Here are some things to consider:

·        At the first indication of a fire, it is vital that we don our full-face mask.   What is the first indication?  Often it is just the smell of smoke or fumes.

·        Every situation is different, but when reading the accident reports, the risk of waiting for a secondary indication is clear.  If you smell fumes, you do not have to wait for visual confirmation or any warning systems.   In the event of a fire onboard an aircraft there is not much time.  SR111 lost a few minutes trying to confirm the indications before initiating a divert.  Did those minutes cost them their lives?

·        Can you get the oxygen mask on within 4 seconds with your eyes closed?  Ensure that your mask is clear of fumes?  This may require using the Emergency position of the oxygen mask long enough that there is no doubt that it is clear.  Fumes can cause vision problems.  Fumes can be toxic and may affect our neurologic functioning.  Both are, obviously, very bad news when you are trying to fly a jet.

·        Do you know where the Emergency knob for your oxygen mask is?   Can you find that knob and operate it blind while wearing the mask?  While the location of the control is obvious when you are holding the mask in your hand, finding it with the mask on is a different story.  The location (with the mask donned) might surprise you the first time.   You do not want that “surprise” when you need to find it in a real emergency.

·        If you have fumes or smoke, your vision may be impaired.  Smoke in the eyes can make your eyes close.  It is not voluntary.  You cannot open them, no matter how hard you try.  Being able to don your mask and turning it to the Emergency position completely blind could mean the difference between life and death. When was the last time you tried it?  Your next flight might be a good opportunity to try it once or twice.

·        Does your aircraft have a HUD?  Studies have shown that it is possible to see the HUD display even with thick smoke in the cockpit.  Are you one of those that has resisted using it on a normal basis?  A fire would not be the best time to first become accustomed to using a HUD/EFVS.

·        Review the Smoke and Fumes checklist for your aircraft.  Could you run the checklist quickly?  If you are a Captain, would it work out better if you are PF or PM?  Who should be working the radios?  Remember that you will be using the intercom to communicate on the flight deck.  That adds more work than you might expect.  Just like anything else we do, thinking about the scenario in advance can make a big difference.

·        What about the emergency equipment?  Can you reach it from your seated position?   What if you slide your seat back?   What if you get out of your seat, will the oxygen mask hose be long enough to reach the walk-around bottle/mask, fire extinguishers and crash axe?  Can you think of scenarios where it might be important to reach these items, or at least know what you can and cannot do in each of these examples?

·        Do you know where your pack switches are?  Can you find them blindfolded?  How fast can you pull together the information you need to divert?

What about cockpit windows?  Should you open them?  Generally, unless the checklist tells you to open them, be very cautious with this.  The windows may create a suction to draw smoke forward and make the situation worse.  If the checklist does tell you to open the window, that indicates that the issue has been studied for your individual aircraft and found to be helpful.

·        As indicated in the FAA study, there is a significant advantage to staying high, and fast, until fairly close to the airport.  Not only does that take advantage of the depressurized state slowing the fire, it also reduces the amount of time for the fire to flare as you start down.  Additionally, your fastest ground speeds are usually available around FL250 to 280. 

·        Once you are diverting, how close to the airport can you maintain maximum forward speed?  There are documented cases where crews slowed to 250 kts approaching 10,000 feet, with an in-flight fire.  Those habits die hard. A common debrief item in the simulator exercise is that the crew could have stayed faster, longer.  How much longer?

Perhaps, the next time you find yourself with some extra simulator time, it might be worthwhile to try for yourself to see what you can do and still feel safe.  Try it with the oxygen mask on. 

·        Sorting out that flow when you experience it for real the first time is not conducive to surviving the situation.  Consider giving the oxygen mask and intercom a try sometime enroute.  Working out the details during a routine cruise flight can provide a significant leg up in the event of a real emergency.

·        What kind of “Smoke Barriers” does your aircraft have?  The cockpit door is one such barrier.  The smoke curtain is another, as is a rigid barrier.  When it comes to stopping the smoke, utilize all the barriers you can.  One of successes of the FedEx Express Flight 1406 flight crew was attributed to their ability to keep a smoke barrier (cockpit door closed) in place and, consequently, their flight deck relatively free from smoke until after landing.

·        When you get settled in your seat, take a moment to close your eyes and locate the things you need, in order to exit the aircraft: window latch, crank, inertia reel door, etc. When the UPS flight into PHL touched down, inertia forced the smoke into the front of the aircraft, and the flight crew was blinded by the smoke.

UPS Capt. Jess Grigg, at that time a First Officer and pilot flying, said that he was focused on getting out of the aircraft, and eliminating things that might impede him, so he released his seat belt and tore off his oxygen mask, then couldn't find the door for the escape reel. He managed to open his window, and stuck his head out to get some air, but still couldn't find his escape reel. They were able to escape the aircraft when the S/O found the 1L door, and was able to open it. He now advises crewmembers to check the location with their eyes closed.

Captain Grigg recalled that when doing "smoke in the cockpit" training in the simulator, he found that the exercise always ended when they landed the plane. In real life, he said, landing was nowhere near the end of the deal. He said that when the smoke alarms went off, it was like "somebody threw an angry bobcat into the cockpit." He also said that when he hit the brakes, it was "as though someone had dumped a pail of hot ashes down my collar."

If you assume an RTO on every takeoff, and a missed approach prior to every landing, you are more prepared in the event those options become reality.  Shouldn’t you apply the same proactive approach to a smoke/fire/fumes event?   Unlike any non-normal a pilot will face in his/her career, a smoke/fire/fumes event is the least forgiving.  Your actions have to be correct the first time. 

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[i] FAA Fire Safety Highlights

[ii] AC 120-80 Appendix 3

Windshear Considerations

Windshear

By Captain Shem Malmquist

At least once each year we each return to fly the simulator.  The “game” in the simulator is fairly predictable.  We know what to expect most of the way through – we are more surprised when something has not failed or gone wrong than when it has!  Although the simulator ride itself is fairly predictable, that probably does not significantly detract from the experience, and we will carry our training to the line.  This is largely true because we are really practicing the procedures themselves as much or more than how to fly the airplane.

So, here you are, flying the simulator, and the instructor tells you that windshear has been reported in the area.  You are now spring loaded to go for the recovery and at the first indication of windshear you go through the escape drill.  But how much is this like the real world?

Recently I was discussing this issue with a friend of mine, TWA (Ret). Captain Steve Holmes. Steve used to teach in the simulator for TWA.  It turned out that we had each encountered a dry microburst on approach, and coincidentally they were while flying into the same airport, SLC.  Another thing that both of us found similar was the insidious nature of the encounter.  Our experiences were virtually identical.

Approaching the Salt Lake area there were some buildups in the area, along with visible VIRGA.  The conditions at the airport itself looked fine, so we continued the approach.  No windshear had been reported.  On final the air was smooth and as we descended on the ILS in virtually unlimited visibility all seemed normal.  The microburst did not slam us all at once, unlike what I have usually experienced in the simulator.  Instead, I found that we kept getting a little bit slow, so had to add a bit of power.  Not a lot, just a bit, but after a while we had a whole lot of power.  At some point it became clear that things were not right and a missed approach was executed. 

The point here is that it was not immediately clear that this was a windshear encounter.  Captain Holmes and I both felt that it was almost like being “sucked in”, in that everything felt and seemed fine until we were fairly committed to flying through the event.  In both of our encounters we felt that we were directly under a newly developing microburst, so encountered the decreasing performance portion only.  He found it particularly disturbing that it could be so easy to get “sucked” into this type of situation as he trains crews to avoid and escape from such encounters in the simulator.  He is very familiar with the procedures and warning signs.

It might be possible to train windshear differently, but that is not the purpose of this article.  It is simply not possible to train for every possible combination of circumstances we are likely to encounter. The responsibility for a safe operation will always rest with the flight crew, and it is our knowledge and experience that keep flying safe.

Temperature and Wind Effects on altimetry

Cold Temperature Corrections

 By Captain Shem Malmquist

Barometric altimeters are prone to various errors. Most pilots understand the effects of non-standard pressure. We correct for this below transition altitude by setting the local altimeter setting as provided by ATC. We are not concerned with it above transition as the altitude is high enough that any errors will not result in loss of terrain separation. To ensure traffic separation, the U.S. has established a chart of “lowest useable flight level”. In other countries this is handled either the same way, or by providing a buffer area, or transition area, between the boundary of transition altitude and transition level.

Altimetry can also be affected by temperature. The old adage “high to low, look out below” applies to temperature as well as pressure. As the temperature increases above ISA, the altimeter will indicate that you are lower than you actually are, and when it is colder than ISA it will indicate that you are higher. It is the latter that gives us concern.

This issue is not addressed in FAA procedure or airway design, although the USAF and Transport Canada do provide guidance, as does FAA in the AIM. Essentially, cold air leads to a denser airmass.  As a result, the pressure as you move higher in the airmass changes faster than under ISA. Instead of dropping one inch per thousand feet, the rate of change is somewhat more. The effect is that the actual pressure at a given altitude is less than it would be otherwise, and, so when you are at that altitude the altimeter will read too high.

The altimeter setting at the field will be accurate, but the further away you get from the reporting station, the more inaccurate it becomes.

The effect on the crew is that they are still aiming to be at a designated indicated altitude when flying a SIAP, a SID or a STAR. However, that altitude does not take into account the effects of temperature. As always, it comes down to the crew to determine the minimum safe altitude for the particular operation. Naturally, we should never rely on ATC for terrain clearance (it is not their job unless you are on a radar vector), and in this case ATC has no way to determine your true altitude.

How do you determine what the correct altitude should be? Well, many of the old “wiz wheel” E6B and similar flight computers have the capability of making the correction from calibrated to true altitude, so that is one way. Another would be to use the chart found in the AIM TBL 7−2−3.

How serious an issue is this? Well, that depends on how cold it is or how far above the reporting station you are flying. Essentially, the colder it is or the higher you are, the worse it is. For example, an ambient temperature of minus 40c will put you almost 200’ low at 1000’ AGL. If you are crossing a ridge line 10,000 feet above the station and it is minus 18c (not that cold for 10,000’), you are actually 500 feet lower than your altimeter is reading. Now, in some locations with a very high airport, imagine the error crossing an adjacent ridgeline. For example, crossing the Rocky Mountains going into DEN, you might be 10,000 feet above the airport at 15,000 feet. A wintertime temperature of minus 30c at 15,000 is not unreasonable.  This scenario will result in you being almost 1,000 feet lower than you think you are – and that is ignoring any local venturi effects of the winds over the ridgeline.

Remember, the formula is only dependent on your actual OAT, and how high you are above the reporting station. The higher the airport elevation the worse the effect will be due to the lower temperature associated with the airport elevation.

Altimeters can also be affected by strong winds across terrain. This factor should be considered when an approach procedure is designed, and it is possible that the lack of such consideration was a factor contributing to the AA accident at BDL a few years ago.  Altimeters are affected by the venturi effect of winds blowing across terrain.  The winds create a localized “low pressure area”, and as we all learned, “high to low, look out below”.  This is obviously only an issue when there is terrain present to create the effect, as there was on runway 15 at BDL.  Consider backing up your barometric indications with radar altitude, if possible, and be generally aware of altimeter errors.  The following chart provides some insight to the extent of wind errors:

       Windspeed* (kts)                     Altimeter Error (ft)

20	56
40	201
60	455
80	812

*Windspeed values were measured 100 ft above airport elevation

Does flying faster to the FAF really save time?

Stabilized Approaches

 By Captain Shem Malmquist

There has been much emphasis on the importance of the stabilized approach.  I recently came across an interesting analysis of the time saved by flying an approach at higher speed as opposed to configuring early.  UPS pilots flew three simulated approaches in their simulator.  The time from the FAF to touchdown was recorded.  The FAF was 5.6 miles from the end of the runway.  The conditions were:

Flight 1: Fully configured and on speed at the FAF.

Flight 2: Typical approach speeds and stable at 1200 AGL.

Flight 3: Speed 250 knots to the FAF and not stable until 100’ AGL.

Following are the times from the FAF to touchdown:

Flight 1 = 2:30

Flight 2 = 2:20

Flight 3 = 2:02

That’s right!  The time “saved” by flying the very fast approach only saved 18 seconds as opposed to being configured and on speed at the FAF! 

Granted, flying a bit faster seems to save time.  Perhaps that is more because the challenge of the late configuration keeps us more occupied.  However, the reason that the approach is more challenging is the same as why the approach increases the risk.  You are not doing yourself any favors by keeping your speed up!

Cold Fuel - Long Range Jet Transport Operational Considerations

Cold Fuel

By Captain Shem Malmquist

                   With special thanks for the information provided by

Captain Phil Simon, UAL (Ret), portions of which have been

reprinted here with permission.

GENERAL INFORMATION

Flight through polar regions is a fact of life of global flight operations. Pilots operating flights on these routes should be aware of issues that may affect flight safety and schedule reliability due to Jet A fuel “Freezing Point” limitations.  UAL tracks the fuel temperature data for their fleet.  Last year 55% of UAL flights in polar regions had fuel temperatures below -35°C.

UAL uses automatic fuel data collection on some of their B-747-400 and B-767-300ER aircraft. Fuel tank data is collected and down-linked to their fuel department, via the ACMS system using ACARS. The reports are triggered when fuel reaches -35°C and are sent every 10 minutes as long as the fuel remains at this temperature or colder. UAL has had a few flights operate for three, four and even five hours with a cold fuel situation.

Cold fuel temperature events are defined as times when the fuel in the aircraft’s tank has reached a temperature of -35°C or lower. Data collected on some long range flights indicates a trend towards more fuel tank cold temperature events.

COLD FUEL TRENDS

In the U.S. the jet fuel most commonly used is Jet “A”; it has has a -40°C freezing point and is used outbound to foreign destinations. The cold fuel trend shows an increase in the number of events for flights departing from the U.S.                              

The trend in the number of events with Jet “A-1” fuel is unclear. This fuel has a -47°C freezing point and is boarded internationally and used inbound to the USA.

In the winter of 91/ 92, enroute temperatures on the London/Tokyo route, using Jet A-1 fuel, showed that:

   41% of flights reached -37°C; for an average period of 3.5 hours and a maximum of 7 hours.

27% of flights reached -40°C for an average period of two hours and a maximum of 4.7 hours.

03% of flights reached -44°C for an average period of 1/ 2 hour with a maximum of 1.25 hours.[1]

On four Chicago to Hong Kong polar route “demonstration” flights conducted last winter the OAT reached -70°C, and fuel tank temperatures reached -38° to -41°C. The actual fuel freezing point was measured at -44°C.

FUEL TEMPERATURES

In the majority of cold fuel events, the fuel has not reached the critical temperature where crystals appear. However, there have been a few flights where this could have happened. For the 1998-1999 reporting period the breakdown for 204 events for flights using Jet A is as follows:

       132 fuel temperature reports at -35°C

         32             “    “            “    “        -36

         16  “          “          “     “    -37

         15  “          “          “     “    -38

          7   “          “          “     “    -39

          1   “          “          “     “    -40

          1   “          “          “     “    -41

None of the 71 events reported for flights using Jet A-1 fuel have had temperatures below -39°C.

                                                             

CITY CLIMATE DATA FOR COLDEST MONTH ON POLAR ROUTES

                              Alaska                         Mean °F/ °C    Record Low °F/ °C

     Barrow                 -25/ -32                         -52/ -47

    Canada               °F/ °C                           °F/ °C

     Churchill              -27/ -33                         -57/ -47

     Frobisher Bay     -23/ -31                         -50/ -46

     Resolute              -36/ -38                         -65/ -52

     Yellowknife          -23/ -31                         -60/ -51

                                  Russia                             °F/ °C                             °F/ °C

     Khatanga            -34/ -37                         -63/ -53

     Yakvtsk                -47/ -44                         -74/ -59

     Mirny                    -32/ -36                         -72/ -58

     Norlisk                  -26/ -32                         -69/ -56

While all of the following airports provide Jet A, notice that there is significant variation in the fuel freeze points.   Not all fuel is created equal, and different airports get different mixes.  As you can see, Jet A from some locations may give you more margin than others.

            JET FUEL FREEZING POINT DATA AT U.S. AIRPORTS[2]

          City                     Typical, °C                         Range

          New York                -45                            -41.5 to -47.5

          Los Angeles           -50                            -46.8 to -58.2

          Miami                       -47                            -41.1 to -52.5

          Chicago                   -43                            -41.5 to -44.7

          San Francisco        -45                            -44.0 to -56.1

COLD FUEL PROBLEMS

With cold fuel events there is risk and exposure to operational problems due to the fuel reaching its specification freezing point limit. The fuel temperature limit for Jet A fuel is -40°C. However, the Flight Operational limits are set at -37°C. This 3° delta “T” is to allow for errors in the fuel temperature probes, the wiring harness, the processor, and temperature gradients in the tank.

It is interesting to note that most countries supply Jet A-1 fuel which has a fuel specification limit for freezing of -47°C; most U.S. military fuel specifications require a limit of -46°C or lower, and the Russians, with lots of cold weather operating experience, specify fuel that is good down to at least -50°C, with some as low as -60°C.

When operating at the specification freezing point limit of the fuel there is the risk of the fuel forming solid crystals of frozen fuel. Fuel does not freeze solid like an ice cube; but rather, the paraffins turn into a semi-solid mush with a porridge-like consistency as the temperature gets colder. This area is called a “low convection ‘mushy’ zone”.[3]  When the fuel reaches its pour-point[4] temperature it will start to freeze along the bottom skin of the wing fuel tanks. Unfortunately, this is where the fuel pump inlets and the flapper valves in the fuel tanks are located. The fuel temperature probes are located 6 to 8 inches above the bottom of the tanks, and therefore may not measure the coldest fuel temperatures. To date Boeing has had no incidents resulting from frozen fuel; however, Airbus has (this could also have been a frozen water crystal problem). This may be due to the fact that Airbus aircraft have had a finer mesh screen on the inlet to the fuel pumps.

FLIGHT CREW CONCERNS

Although the CFM covers cold fuel operations, there are some additional concerns and training issues for flight crew members when dealing with very cold fuel situations. Crews should be informed that :

a.       Low fuel temperature is a concern for fuel flow to boost pump inlets and through fuel lines. Fuel may not be able to get to the fuel pumps and is therefore not available to be burned. The fuel pick-up screens are located at the bottom of the tanks, and although the fuel in this area may become frozen there have been no problems with pump starvation to date. This is due to the high flow to the pump, which results in a clear path through the frozen fuel. Photographs of this path show it looking like a vortex or mini tornado of liquid passing through the paraffin crystals to the boost pump inlet.

b.       The flapper valves in the webs that separate one section of the tank from the next, may be prevented from moving due to frozen fuel. This would prevent all of the fuel in a tank from reaching the fuel pump inlet, resulting in a situation where there is fuel on board but it is not available to be burned.

c.       When reaching the destination or a diversion airport, the crew may have a scenario where not all of the planned reserve fuel will be available, since part of it may still be frozen and therefore not able to be used for holding or diversion. The exact amount of this unavailable fuel is not known at this time. This is presumed not to be too significant as the frozen layer of fuel may not be very thick. The exact amount is a function of the area of the lower surface of the fuel tank.

d.       Crews should be made aware that fuel tank temperature can drop rapidly when the aircraft enters a cold air mass. The rate at which the fuel temperature declines is a function of air temperature, airplane geometry, fuel management schedule and flight time.[5]  It is possible for the aircraft skin temperature to reach -70°C. Crew training should include the need to react aggressively to counteract this situation. Descending into warmer air and increasing speed may not be effective. Additionally, because of the large mass of the fuel, the fuel will not warm back up for some time, even though the dome of cold air has been passed.

e.       The pilot sees ambient air temperature (OAT or SAT), total air temperature (TAT) and fuel tank probe temperature. TAT is a function of ambient air temperature and Mach number. TAT can be used to estimate main tank bulk fuel temperature.

f.        The CFM requirement is to keep the main tank fuel temperature above the fuel freezing point plus 3°C.( e.g. Jet A: -40°C + 3°= -37°C; Jet A-1:  -47°C + 3°= -44°C.)

g.       Actual fuel freezing point varies from the published fuel specification limit. Fuel that is all Jet A-1 or has a large part of Jet A-1 mixed in, will have a lower freezing point. This may actually reach -50°C for some Jet A fuel; other Jet A fuel may have a freezing point at it’s specification limit of -40°C.

h.       Fuel at various airports will have different freezing points depending on the supplier. The highest density fuel available anywhere comes from the west coast of the U.S. Aircraft fueled at SFO or LAX can reasonably expect their fuels to have an actual freeze point around

i.         -49°C to -58°C. On the other hand, fuel boarded at ORD consistently has a freezing level around -43°C to -44°C. Miami fuel varies greatly as its fuel supply comes from many sources and at times has lots of Jet A-1 mixed in. The freezing point can vary from -42°C to -52°C in just one day. Some of the lightest density fuels come from Southeast Asia, these will have the highest freeze point temperatures (i.e. Jet A fuel will freeze at the specification limit of -40°C instead of -50°C).

PILOT ACTIONS in COLD FUEL SITUATIONS

Pilots must take action to keep the fuel warmer than 3°C above the fuel freezing point. If the pilots do not know the actual freezing point of the fuel on-board they must assume specification maximum (Jet A -40°C, Jet A-1 -47°C). Corrective actions are to increase Mach number, and/ or fly at a lower altitude, and/ or divert around the cold air mass.

Fuel temperatures will be slow to respond to corrective actions because of the fuel mass. For the B-747-400 it takes approximately ten minutes to change the fuel temperature by 1°C. In an extreme case an aircraft may have to descend to 25,000 feet and increase airspeed to Mmo. [6] 

Aircraft operating on polar routes will need to take corrective action to stop fuel temperature decline on some flights when using Jet A fuel which is at the specification freezing point.[7]  Current diversionary action is to fly faster, fly lower (or higher), or to divert around the cold air mass. Review Cold Fuel Procedures. General Information:

Recall that with extremely cold conditions, the tropopause will usually occur at lower flight levels. When the fuel temperature approaches the limit, consideration should be given to descending or climbing to a warmer altitude. The Standard Air Temperature above the tropopause is approximately -57°C Celsius. Mach .84 provides approximately 31 degrees ram rise, resulting in a Total Air Temperature of -26°C.

Ram rise is defined as the influence of air friction and compressibility on the temperature of the aircraft skin. Total Air Temperature is the temperature “seen” by the aircraft. Fuel temperature mirrors Total Air Temperature after a delay but will not decrease to a value below the Total Air Temperature. For example, if a Total Air Temperature of -42°C is encountered, the fuel temperature can drop to -42° in a little as 30 minutes if an altitude or speed change is not made.

Vertical temperature distribution shows that air cools in a straight line from 10,000’ to 30,000’. Above 30,000’ the air temperature drops very little. The mean temperature at 10,000’ at 65°N 110°E over Siberia in the winter is -27°C; this drops to -55°C at 30,000’.  Some strategies include:

a.       Flying Faster:  Increasing cruise speed from Mach .83 to .85 will provide one degree additional ram rise. In other words, increasing speed one Mach number (.01) will raise the fuel temperature about 1/ 2 degree. It is very likely that you will be unable to fly fast enough to make much of a difference.

b.       Flying Lower: For a flight crew to descend to a temperature warmer than -40°C, they would have to descend to an altitude below 25,000’. Descending this low will drastically increase your fuel burn. It is very likely that this option is not a good choice.

c.       Diverting: The best solution is to fly away from the dome of cold air. In order to do this flight crews need to be provided with a weather chart showing the locations of these domes.

TECHNIQUES USED BY OTHER OPERATORS

       1.    When fueling with Jet A-1 KLM requires that before fueling, any Jet-A fuel on board be transferred to the center wing tanks. This ensures that the wing tanks, which have more exposure to cold temperatures, will be loaded with Jet A-1 fuel.

       2.    Some operators conduct planeside fuel freezing point testing for flights operating in cold weather.  Presently the fuel has to be taken to a lab and tested. The results are then sent via ACARS to the flight crew.

      

CONCLUSIONS

              Data confirms that Jet A fuel may not meet long range international flight operational requirements when low air temperatures are encountered enroute.[8] Ambient temperatures can reach -77°C on polar routes. Fuel temperatures can and do reach            -44°C. Therefore, fuel with -47°C

              (or lower) freezing point (Jet A-1), MUST be available for some polar routes on certain days or the flights will have to be rerouted.  As our routes include more long haul and polar routes, fuel data for our fleet should be tracked and that information provided to flight crews.  If fuel temperature appears to be a problem, then consider incorporating the following:

1.   Jet A-1 fuel should be delivered to selected U.S. gateway airports.

2.   Aircraft flying on a polar route should be provided the actual freeze point of their fuel.

3.   Use our meteorology department to help identify areas of very cold air masses. Coordinate sharing this information about cold regions of air between Meteorology and GOC.

4.   Crews should refer to the WSI “North Pole Temp/ Trop Prog 250MB” and the “North Pole Sig Wx Prog” charts.

5.   GOC should learn to route flights to avoid these areas of extreme cold air instead of staying on the best wind routes.

6.   Consideration should be given to testing the fuel as it is put on our polar flights and informing the crew of the exact freezing level for that load of fuel. This may require uplinking the test results to the flight crews using ACARS, since the results currently are not immediately available and must come from a laboratory.

7.   Use low freeze point fuel for aircraft routes requiring protection.

8.   Develop a “Cold Fuel Training Program” for flight crews flying polar routes and a “Cold Fuel” handout for flight crews flying polar routes.

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[1] Information from September, 1999, Boeing,  presentation “Jet Fuel properties-affect on Long Range Operations...”

[2] Ibid; source Phase Technology

[3] Ibid.

[4] Pour Point is the point where there will be no flow from a 1.5-inch cylinder.  At 4 degrees below the “freeze point” the fuel will reach a point where some fuel will not flow, and as it continues to cool it eventually reaches the pour point.

[5] Information from September, 1999, Boeing,  presentation “Jet Fuel properties-affect on Long Range Operations...”.

[6] Ibid.

[7] Ibid.

[8] Information from September, 1999, Boeing,  presentation “Jet Fuel properties-affect on Long Range Operations...”