The Gulfstream crash at Hanscom Field

Friends have been asking me about the crash of N121JM, a 2000 Gulfstream G-IV, after running off the end of Runway 11 at Hanscom Field on Saturday evening (Boston Globe). I didn’t know any of the people involved, I don’t have a Gulfstream type rating, and at this point the most that anyone can do is speculate. However I will share with readers what I have shared with friends, mostly based on my experience flying the Canadair Regional Jet, a similar size aircraft.

Background: In theory, you take off in a twin-engine turbojet by holding the brakes, pushing the thrust levers forward, verifying that you’ve reached full power, and letting go of the brakes. The pilot flying looks down the runway. The pilot monitoring checks the airspeed indicators on both sides and says “100 knots cross check”. Then the pilot monitoring calls out “V1“. This is the “decision speed”. If an engine quits before V1, you pull the thrust levers back, hit the brakes and stop before running off the end of the runway. The FAA allows about one second as a reaction time and assumes near-perfect technique after that. This is the reason that commercial airport runways are so long. The plane needs enough runway to come within 1 millisecond of taking off and then enough runway to brake to a stop from 150 miles per hour or so. If an engine quits and you’ve reached V1 you continue the takeoff on one engine. You wouldn’t be at that airport with that load of passengers and fuel if the dispatchers hadn’t calculated your ability to take off and climb out to clear obstacles on one engine (i.e., you won’t be able to carry as much weight if taking off from a high altitude airport surrounded by mountains, since turbojet engine power output falls as altitude increases).

Takeoff configuration: The CRJ simply would not take off, even from a 15,000′ runway and with full power, unless flaps were extended. The clean wing was designed to minimize drag during high-speed cruising. Thus it is critical to have the flaps properly configured for takeoff or the airplane will simply keep accelerating down the runway without lifting. All of the standard performance charts for the Gulfstream G-IV assume “flaps 20″ but the NTSB reports so far have described the flaps being set to just 10 degrees in the cockpit (given that the plane supposedly reached 165 knots, it should still have been able to lift off at flaps 10).

Refinement 1: In the real world, pilots aren’t that great at aborting takeoffs and it is hard on the airplane’s systems to slam to a stop once the plane reaches about 115 miles per hour. So at our airline we had a rule that unless it was something pretty dire we would continue the takeoff once we reached 100 knots and then work out the problem in the air.

Refinement 2: Passengers prefer a “rolling takeoff” in which the brakes are not held as the thrust levers are advanced. Unless one is operating from a short runway in the mountains, this is how take-offs are typically done. Unfortunately this chews up additional runway due to the plane rolling as the engines “spool up” to full power. For the CRJ, no data are available regarding exactly how much runway is wasted in this fashion and whether or not the plane can still be stopped after recognizing a problem at V1. A friend sent me a portion of the Gulfstream G-IV Airplane Flight Manual (AFM) and it seems to indicate that the performance charts can be relied upon even given a rolling takeoff.

Refinement 3: In the real world, a twin-engine turbojet has way more power than it needs for most flights. If you’re lightly loaded (few passengers, short trip so not too much fuel) and departing from sea level, why would you want to make those engines work so hard? The FAA Advisory Circular AC 25-13 from 1988 explains that “Takeoff operations conducted at thrust (power) settings less than the maximum takeoff thrust (power) available may provide substantial benefits in terms of engine reliability, maintenance, and operating costs.” An additional advantage of reduced thrust is that passengers on a lightly loaded plane won’t be slammed back in their seats like astronauts.

If you’re an engineer you would naturally assume that this would all be idiot-proof on a $50 million plane stuffed full of computers. The airplane infers its departure runway and airport altitude from the GPS location and heading. You push a button for “reduced thrust”, the airplane reads its weight from the strain gauges on the landing gear, and then you advance the thrust levers fully when you’re ready to go. The airplane will make sure that the flaps are set properly and if one engine stops developing thrust the other one will automatically advance to full power. If you lived to be 1000 years old you would probably not be able to get this design certified by the FAA (for the same reasons that the FAA-run air traffic control system will not send your airplane a text message with the instrument flight plan waypoints; instead a controller will read it to the pilot over the radio and the pilot will enter a bunch of 5-letter waypoints and 3-letter VORs into a GPS (possibly getting them wrong)).

In real life what happens is that the pilots calculate the aircraft weight (we did it on paper back in 2008!) and then use a paper chart or maybe an iPad app to calculate the proper reduced thrust setting. If there is a error in this calculation or the transcription from the calculation or the entry of the airport/runway, the resulting thrust might not be enough to become airborne. This is a serious problem because pilots are making the go-no-go decision primarily on aircraft speed (V1 yet?) not based on how much runway is left. The assumption is that the calculations have ensured that the runway length will be sufficient for all possible events. And of course the actual setting of the thrust requires the pilots to watch gauges, another opportunity for misinterpretation. The airplane, though equipped with a GPS, does not have a warning such as “You’ve got 2000′ of runway left. Maybe it is time to go to full power?”

Can a pilot get this wrong? Sure. In fact, four pilots can get this wrong, as demonstrated on March 20, 2009 by Emirates A345, an Airbus A340-500 departing from Melbourne (official report). A simple data entry error caused a lower-than-sufficient thrust to be calculated and the $200 million airliner ran off the end of the 12,000′ runway, taking out lights and antennae. The Emirates crew made the “go” decision rather than the “stop” decision of the Hanscom Gulfstream. When the end of the runway was near the pilot pushed the thrust levers forward for full power and the airplane then flew quite easily.

Please don’t read this posting and infer that I know anything about why this Gulfstream crashed. The intent is just to answer the question that friends asked repeatedly, i.e., “Is there any way to crash a modern business jet on takeoff without the cause being a catastrophic mechanical failure?” And I am as saddened as everyone else about the loss of life.

[Separately, local pilots have been discussing the safety record of our airport, which has more than 150,000 operations per year. The NTSB database shows that the most recent fatal accidents were the following:

  • 11 years ago: four-seat single-engine Cessna crashed on an instrument approach due to pilot disorientation in the 400' overcast (report from 2003).
  • 16 years ago in a four-seat single-engine Piper that got slow in a turn and suffered an aerodynamic stall after a 4.5-hour flight (see this NTSB report from 1998)
  • 30 years ago: four-seat single-engine Piper crashed due to spatial disorientation on an ILS, almost identical to the 2003 accident (report from 1984)

]

17 Comments

  1. hcsitas

    June 3, 2014 @ 1:14 pm

    1

    Brings back memories of Northwest in Detroit. Can’t believe the technology that sounds an alarm for disengaged seat belts hasn’t made it to yet to private jets owned by millionaires. Or has it? If I bought my own jet, could I have flap-alarms add as an option?

  2. Kourt Bailey

    June 3, 2014 @ 2:53 pm

    2

    IIRC, the DC-9 in NW255 had a warning system, but it activated during (routine) single-engine taxi operations so crews (routinely) pulled the P-40 breaker to disable it. Of course, the day you forget to set the flaps & slats is the day that you forget to re-enable the warning.

    Reduced power takeoffs are a completely different (and more analog) failure mode.

    The idea of load sensors is good: I’ve long wondered why they aren’t used to detect an aft center of gravity more reliably than the 150 pound passenger assumption.

  3. Kourt Bailey

    June 3, 2014 @ 2:59 pm

    3

    Actually, it’s not certain whether the NW255 breaker was pulled, or malfunctioned:
    http://lessonslearned.faa.gov/ll_main.cfm?TabID=2&LLID=69&LLTypeID=2

  4. Susan F

    June 3, 2014 @ 6:05 pm

    4

    Thanks Philip. Nicely written so “regular folk” can understand!

  5. Izzie L.

    June 4, 2014 @ 9:00 pm

    5

    >All of the standard performance charts for the Gulfstream G-IV assume “flaps 20″ but the NTSB reports so far have described the flaps being set to just 10 degrees in the cockpit (given that the plane supposedly reached 165 knots, it should still have been able to lift off at flaps 10).

    Is there any good reason why you would set the flaps at 10 when the checklist call for 20? I could see possibly missing setting the flaps completely, but if you remembered to set them, why would you set them for an incorrect value? Is it possible that the flap setting changed as a result of the collision or that the pilots tried to move them when they aborted the takeoff? If you abort before V1 are you supposed to change the flap setting?

  6. Izzie L.

    June 4, 2014 @ 9:18 pm

    6

    Regarding the Emirates tail strike, I realize that no matter how long you make the runway, it has to end at some point, but wouldn’t it be wise NOT to put light poles, antennas, etc. in the area beyond the end of the runway (or to construct them in a way that they would break away rather than damage the aircraft)?

    Also, I recall reading about an experimental material that was sort of a cross between styrofoam and concrete that was meant to be used at the end of runways – the idea is that the wheels of the plane would partly sink into this stuff and quickly come to a stop as it tried to plow through it. This was after a couple of incidents at LaGuardia where the plane ran off the end of the runway and ended up in Flushing Bay. Did anything ever become of that idea?

  7. Izzie L.

    June 4, 2014 @ 10:12 pm

    7

    More information here (though it sounds like the reporter confuses flaps and elevators):

    http://www.philly.com/philly/news/nation_world/20140605_NTSB_examines_jet_s_flight_controls_in_fatal_crash.html

  8. Kourt Bailey

    June 5, 2014 @ 1:09 am

    8

    Izzie, search for “Engineered materials arrestor system” (EMAS). It’s currently installed on 74 runways at 47 airports (some of which serve general aviation), with more installations planned. The benefit is minimal at runways which meet modern standards for paved overrun areas and have favorable surrounding terrain.
    http://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=13754

    There is only one FAA-approved supplier: this probably leads to an unusual proposal process.

    Many of the lights and antennas that you find at runway ends need to be there, e.g., “Runway End Identifier Lights”.

  9. philg

    June 5, 2014 @ 8:09 am

    9

    Izzie: Why would you ever do a Flaps 10 takeoff? http://code7700.com/g450_takeoff_flap_selection.html shows an example. I think the G450 is pretty much the same airframe as the G-IV. “The lower setting gives you a better climb but takes more runway, the higher setting gets you off the runway sooner at a cost of some climb performance.” In the CRJ, for example, we were trained to use reduced flaps (Flaps 8 instead of Flaps 20) taking off from long runways at high altitude that were surrounded by mountains. That’s not Hanscom Field, obviously, but the professional pilots at http://www.pprune.org/biz-jets-ag-flying-ga-etc/540858-gulfstream-iv-bedford-ma-3.html talk about using Flaps 10 and reduced thrust to “give their passengers a smoother take-off and less steep initial climb out angle”.

  10. Izzie L.

    June 5, 2014 @ 8:42 am

    10

    >Flaps 10 and reduced thrust to “give their passengers a smoother take-off ….”

    I have the sneaking suspicion that VIP Syndrome somehow contributed to this crash. This occurs when VIPs (and those around them) begin to believe that they are not only exempt from rules applicable to ordinary mortals like having to wait for a table at a restaurant but that they are also entitled to be exempt from the laws of physics.

  11. philg

    June 5, 2014 @ 9:09 am

    11

    Izzie: Lending some credibility to Thomas Piketty’s book, having a 14-year-old Gulfstream does not qualify for VIP status at Hanscom Field. That is solidly “middle class”. (Our helicopters shared a hangar with a G-IV (subsequently upgraded to a G-450) and the mechanic gave us a tour of the interior. I asked “Are those seat belt buckles actually gold?” He responded “Of course not. They are only gold-plated.”)

    A G-650, a BBJ, or an executive configuration 767 might qualify as VIP transport at KBED.

    Anyway, I am not aware of a “VIP passenger” section of the checklist on a G-IV and trying to keep Delta passengers comfortable is something that we did even in our tired CRJs. Operating a G-IV from a 7000′ runway on a clear night does not at first glance appear to be a decision that was made unwisely or because of pressure from a VIP.

  12. Tony Rowlett

    June 5, 2014 @ 3:01 pm

    12

    I want to echo Susan F’s comment; thank you, Philip, that was a cool read. Most of those things I never knew. Quite interesting. And, actually, I think it would be way cool to be sucked back into my seat on takeoff instead of just the “rolling” version!

    p.s. Mimi and I send our best regards and hope you and family are doing well!

  13. Mike S.

    June 7, 2014 @ 9:17 am

    13

    Whenever a powerful aircraft fails to lift from a runway, my first thought is takeoff configuration problems. Apparently both engines were performing as expected, so we can only assume a flap problem.

  14. Miles D East

    June 11, 2014 @ 3:14 am

    14

    “If you’re an engineer you would naturally assume that this would all be idiot-proof on a $50 million plane stuffed full of computers. The airplane infers its departure runway and airport altitude from the GPS location and heading.”

    Most new aircraft can do this using a system called “RAAS”. It then uses a synthesized voice to tell you which runway you are on.

    “You push a button for “reduced thrust”, the airplane reads its weight from the strain gauges on the landing gear, and then you advance the thrust levers fully when you’re ready to go.”

    Most new aircraft can do this. It is called “Flex Thrust” and you do indeed just push a button to enable this mode. The FMS calculates what the additional runway penalty will be and advises the crew. Ditto for crosswind rolling takeoff.

    “The airplane will make sure that the flaps are set properly and if one engine stops developing thrust the other one will automatically advance to full power.”

    Most new aircraft have this capability if they are also equipped with auto throttles. They also will generate a warning when the throttles are advanced, if the current configuration is not correct.

    If you lived to be 1000 years old you would probably not be able to get this design certified by the FAA (for the same reasons that the FAA-run air traffic control system will not send your airplane a text message with the instrument flight plan waypoints; instead a controller will read it to the pilot over the radio and the pilot will enter a bunch of 5-letter waypoints and 3-letter VORs into a GPS (possibly getting them wrong)).

    Most new aircraft have been certified with all of these features.

    The filed flight plans and ATC approved changes to the flight plans are uploaded automatically through a system called “ACARS” and you just have to press one button to accept the flight plan and all of its waypoints.

  15. philg

    June 11, 2014 @ 8:11 am

    15

    Miles: I’m aware of the stuff that you cite, but not that it is all integrated into one package. And the critical feature of the airplane reading its own weight does not exist, as far as I know. (Hence the incident in Australia that I mentioned, in which the super modern A340 did everything automatically but using a miscalculated or mistyped weight.)

    You can see the lack of integration in http://www51.honeywell.com/aero/common/documents/egpws-documents/raas-documents/SmartRunway_SmartLanding_description.pdf for example (describes the RAAS system). It says that “On-Ground Advisory provides the crew with awareness of which runway the aircraft is lined-up with, and that the runway length available for takeoff is less than the defined minimum takeoff runway length.” Instead of looking at weight, weather, altitude, etc., it seems just to be looking at a hard-coded number. Also look at “The Approaching Short Runway – In Air Advisory does not take into account aircraft performance factors such as aircraft weight, wind, runway condition, slope, air temperature and altitude of airport.” (i.e., it is as dumb as a brick, since a 5000′ runway at sea level on a cold day is a different animal than a 5000′ runway at 8,000′ on a hot day)

    Right in the same document it talks about the “Altimeter Monitor” where the airplane wants if the flight crew has not set the altimeter to non-standard/standard values depending on altitude. Given that the altimeter entry in modern avionics is digital and that avionics can receive nearby airport altimeter settings digitally, why is the big innovation this alarm system instead of a system where the airplane figures out the proper altimeter setting and sets it?

    Also see “The design of RAAS does not include knowledge of ATC clearance and/or flight crew intent, and therefore factors such as clearance misunderstandings; incorrect/inappropriate clearances cannot necessarily be mitigated by use of RAAS.” (so if the Tower cleared you to take off from Runway A and you are on Runway B, which is also sufficiently long, the RAAS will be happy) and “RAAS does not include knowledge of prevailing Notice to Airmen (NOTAM) and therefore factors such as closure of runways are not reflected by advisories.” (so one part of the avionics will receive a digital transmission of the fact that Runway 9 is closed and the RAAS will sit quietly while the plane lines up to take off on Runway 9)

    If the problem is that the airplane doesn’t have an integrated idiot-proof system it is hard to believe that the solution is adding 10 non-integrated automated systems to the airplane, all beeping at the pilots at different times with different tones, and none equipped with even the knowledge of a 40-hour Private pilot (e.g., that hot temperatures and high altitude will affect aircraft performance).

  16. Ron Rapp

    June 11, 2014 @ 12:00 pm

    16

    The G-IV and other Gulfstream models (IV-SP, G300, G400) with the SPZ-8000/8400 avionics have a takeoff configuration alarm which consists of an audible alert accompanied by a red CAS message to alert the pilots of an improper configuration if the power levers are advanced beyond a certain point.

    Flaps 10 is an approved takeoff setting, but I’ve never used it or known anyone who has. Accompanied with a flex power takeoff, the balanced field length might have been near 5000 feet.

    I don’t know what caused the crash, but the NTSB reported that they attempted to rotate and couldn’t get the nose up. The CVR contained comments about control issues, so it seems possible that this was a mechanical failure.

  17. Pierce

    June 12, 2014 @ 12:10 am

    17

    most flight crews check flight controls for freedom of movement prior to take off. I would assume the crew of this flight performed this preflight checklist item also. If it is factual that the airplane reached a speed of 165 knots prior to exiting the end of the runway, and that at rotation speed the nose of the airplane would not lift off the runway…then one can only conclude that the elevator did not move when the pilots pulled back on the control wheel during rotation.

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