A Christmas Miracle
28 Dec 18
I am not a
fan of “miracles” which dismiss the safety culture, training and skill that
airline crew bring to a situation; however, in the case of the Miraklet i
Gottröra, it has to be said that pilot skill was supported by a large helping
of good fortune which led to this amazing happy-ending crash landing in 1991. A
special thank you to Leif Hellström who pointed out this one out to me and
send me plenty of material to get immersed into it. For those that like to
follow along, my primary resource is the SHK (Statens haverikommission or Board
of Accident Investigation) Official Accident Report
released in English.
The accident
happened on the 27th December 1991 in Gottröra, AB county, Sweden near the
Stockholm/Arlanda airport but it started the night before, when the aircraft,
operated by SAS (Scandanavian Airlines), arrived at Stockholm after a night
flight from Zürich.
Accident aircraft in June 1991 taken by Konstantin von
Wedelstaedt
The aircraft
was a McDonnell Douglas DC-9-81, originally known as the DC-9 Super 81 but now
more generally known as the MD-81. The MD-80 series was a development of the
aircraft type DC-9 and the MD-81 is the basic version of this series. A critical
point is that the engines are mounted on pylons on the rear part of the
fuselage rather than on the wing. The engine intake is particularly wide, with
a diameter of about 1.2 metres (almost four feet). This particular MD-81,
registration OY-KHO, was set up for SAS passenger services with 133 passenger
seats and five seats for cabin staff.
On the night
of the 26th of December, Stockholm had snow and rain which lightened to light
drizzle. There was a thin layer of slush on the runway and the temperature was
+1°C (34°F). The flight from Zürich to Stockholm was uneventful but, during the
cruise phase of flight which lasted an hour and forty minutes, the temperatures
dropped to -53°C and as low as -62°C (-80°F). The aircraft landed at 22:09 with
2,550 kg fuel in each wing tank (5,620 pounds), which had become chilled in the
low temperatures of the cruise. The aircraft parked at gate 2 at the
international terminal; its next flight was the scheduled passenger service to
Copenhagen departing at 08:30, just before sunrise.
A technician
checked over the aircraft during the night. He had to clear slush from the
landing gear to be able to inspect it and, at 02:00, now the 27th of December,
he noticed that clear ice had formed on the upper surfaces of the wings, chilled
by the cold fuel in the tanks. He had no instructions to report this to anyone
and he finished his inspection, leaving the aircraft for the mechanic to carry
out the departure check the next morning.
By 06:50, the
temperature had dropped to freezing again. At 07:30, the mechanic responsible
to handing over the aircraft found frost (rime) on the underside of the wings,
which meant a risk of clear ice on the upper surfaces of the wing. The
mechanic climbed up on a ladder and, balancing with one knee on the leading
edge of the left wing, felt the upper side of the wing. There was no ice
there. It was cold and slippery from the rain and so he did not climb out
on the wing but concluded that as he couldn’t feel any clear ice from where he
stood, there wouldn’t be any further along the wing.
He was wrong.
Clear ice
forms on the upper surfaces of wings when there’s high atmospheric humidity or
rain in combination with greatly chilled wings. At the time of the accident,
1991, there had been a number of cases where clear ice had formed on the wings
of the DC-9 type aircraft and then broken off during take-off as the wings
start to flex. The problem with this type, specifically, is that the engines
are to the rear and have a large intake area, so the ice is ingested by the
engines and causes damage to the fan blades and the engines. In 1985, Finnair
released a report on the problem, describing undiscovered clear ice as “the
most difficult systematic threat to flight safety today”.
The following
year, McDonnell Douglas recommended the installation of warning triangles
with indication tufts on critical wing areas. These nylon tufts would not move
if encased in ice, so you could touch them to confirm whether there was clear
ice on the wings. SAS had these installed on their aircraft in October
1987 to help maintenance staff detect clear ice on the wing. By 1989, these
tufts were standard on newly built aircraft.
By 1991,
McDonnell Douglas had offered further modifications: Ice FOD
Alert system (a sensor on the upper side of each wing), Inboard
Refuelling System (new, warmer fuel is mixed with stationary cold
fuel in the inner part of the wing tanks) and Alternate Fuel Burn System
(creates an insulating layer of air between the wing tank fuel and the upper
side of the wing). These modifications were all optional and SAS had not
introduced them to their aircraft with the exception of one trial aircraft. The
modifications became standard on new aircraft delivered from the beginning of
October 1991.
On the 26th
of October 1991, exactly two months before the accident, SAS distributed a
FLIGHT DECK BULLETIN/WINTERIZATION with a special section on CLEAR ICE.
Although the
awareness within Line Maintenance is mostly good, the responsibility again
leans on the P-i-C that the aircraft is physically checked by means of a
hands-on check on the upper side of the wing. A visual check from a ladder or
when standing on the ground is not enough.
Each mechanic
had a checklist which included checking for clear ice by touching the wing
upper surfaces. But there was no further information as to how to verify if the
wing surface was contaminated with clear ice (other than feel the wing upper
surfaces with your hand), how to remove it, and how that discovery should
affect the follow-up check and/or the report to the captain.
On that
morning, there were 6 crew and 123 passengers on board. A further 1,400kg of
fuel (3,000 pounds) was added to the aircraft tanks. The mechanic told the
captain about the frost he’d seen underneath the wings and they agreed that
they should get de-icing on the undersides of the wings. There was no
discussion about the risk of clear ice, although that frost was a specific
symptom listed in the training for both the mechanic and the flight crew.
While the
aircraft was being de-iced, the pilots carried on with routine checks,
including the departure procedure from Stockholm/Arlanda. The captain commented
on the procedure for engine failure, saying “Engine failure follow…2,000…that’s
very general.”
The man operating
the spray nozzle of the de-icing truck said he saw one of the tufts move
(although a passenger seated at the window never saw them move at all). After
he had sprayed the upperside of the wings de-icing fluid, the mechanic
requested further de-icing to make sure that the wings were clear of slush. The
de-icing process used 850 litres of de-icing fluid type 1, which had been
heated to 85°C (185°F).
Type 1
de-icing fluid has a low viscosity (“unthickened”) and provides only short term
protection because the fluid flows off the surfaces. The fluid is sprayed hot
and at high pressure to remove existing snow, ice and frost.
This differs
from the other types of de-icing fluid. Type 2 de-icing fluid contains a
thickening agent to keep it on the surfaces until the aircraft speed reaches
around 100 knots (195 km/h or 115 mph). Type 3 is also thickened to stay on
surfaces but it is used on aircraft with a slower rotation speed, as the the
viscosity breaks down quicker. Type 4 is similar to Type 2 but lasts longer (so
useful if the flight isn’t immediate). These types are more correctly known as
anti-icing because they are used to stop icing from re-occuring after a type 1
de-icing.
As the
temperature was just at freezing, only type 1 de-icing fluid was used. As the
mechanic had not found any clear ice before de-icing, he didn’t see any need to
check again after the de-icing had been carried out. The technician who had
noticed the ice in the early hours was long gone.
Ground crew
reported to the captain that the de-icing was complete. The captain asked if
they had it good and clean under the wings. The mechanic told him yes, there
was a lot of ice and snow, but, he said, “it’s fine now, it’s perfect”.
The captain thanked him.
On the 6th of
December, 20 days before the accident, SAS issued an AOM Bulletin MD-80 which
dealt with a number of issues including the risk of engine damage caused by
clear ice. It said that for certain destinations (with specific airports listed
in Italy and France) there was a greater risk of clear ice problems remaining
undetected because the attention of the ground personnel there could not always
be expected to be the best. Stockholm’s Arlanda airport, on the other hand, had
a great reputation for cold-weather issues and has the distinction of having
never needed to close as a result of snow.
The bulletin
also specifically mentioned that the responsibility for ensuring that the
aircraft is free of ice lies with the captain. It also stated directly that
“rime on the underside of the wing is a good reason to believe that there is
ice on the upper surface during precipitation.”
MD-80
training did not emphasis this issue and there’s no reference to clear ice in
the MD-80 study guide which was used by pilots when training on type. Later,
the first officer said that he had never realised the extent of the clear ice
problem during his training on the MD-80. Also, the AOM walk-around inspection
of the aircraft before flight had no special instruction regarding an ice check
before flying. The checklist had only one reference to ice and snow which was
regarding de-icing with the engines running.
Google maps view of Stockholm/Arlanda Airport with
runway 8 at the top.
The flight
crew taxied the MD-81 to runway 08 for take off. The runway had been cleared
of snow, with just one narrow strip of snow left by the snow clearing
equipment. Both engine anti-icing systems were on and operating in the normal
range. The Auto Throttle System (ATS) engaged. The captain made a rolling
take-off and everything seemed normal until rotation. As the aircraft lifted
off, passengers seated at the windows saw ice coming off of the wings. The
captain heard an odd sound, a humming noise, which he could not identify. Then
there was a loud bang and the aircraft vibrated and jerked, described by one
person as if someone was slamming on the brakes repeatedly.
The aircraft
was at 1,124 feet and in cloud. The flight crew attempted to switch on the
autopilot to gain time for trouble-shooting but the autopilot failed. A voice
warning sounded with “Autopilot” and continued to sound for the rest of the
flight.
The aircraft
vibrations made it difficult to read the engine instruments as the parameters
fluctuated wildly. These instruments had been implicated in an accident just a
few years earlier, the Kegworth accident in England, and it was already known
by then that the shorter electronic hands on the modern instruments were
hard to read. The first officer said “compressor stall” as the captain pulled
the right engine throttle lever back.
A compressor
stall, or engine surge, is when the compressor blades suffer an aerodynamic
stall which results in abnormal airflow. The blades in the compressor are
bound to the same principals as the wing and the propeller: if the angle of
attack on the blades exceeds their critical angle, then the air is not passed
smoothly along. Instead, the air flowing through the compressor is subject to
turbulence and pressure fluctuations and can result in a reverse airflow. A
compressor surge, or surging engine, is when the airflow through the compressor
is completely disrupted. One of the most common causes of compressor stalls is
foreign object damage, such as bird strikes or the ingestion of ice.
The signs of
a compressor stall include an increase in engine temperature, fluctuations in
engine RPM and ‘backfiring’ sounds. The compressor stall can quickly lead to
engine damage and then to engine failure. The most well-known example of
this is probably US Airways flight 1549, in which Captain Sully ditched into the
Hudson River after flying through a flock of geese directly after
take-off.
The correct
response to an engine surge is to reduce the throttle and clear the surge. The
engine should recover on reduced thrust and, with any luck, the aircraft can
continue safely to the airport on one full engine and one with partial thrust.
The captain
reduced the right engine power by ten percent. It didn’t help. Seven seconds
later, the engine surged again and then again three seconds later.
That was
because there was a feature on the aircraft which the flight crew didn’t know
about, which immediately increased the throttle again. The first officer
said, “Think it’s a compressor stall.” By now it was clear that they were at
risk of losing the engine completely.
And with that,
I’m out of time, so I’m going to ask you to come back next week to find out
just what happened!
The Christmas Miracle – Part Two
4 Jan 19
I try to make
these posts as stand-alone as possible but this time I just couldn’t do it. In
order to make sense of this post, you need to read Part One of the Christmas
Miracle here.
So when we
left off, the aircraft had been in the air for under a minute and the right
engine was surging. The captain had reacted correctly, reducing the power for
the right engine, but it had no effect due to a new system that the flight crew
didn’t know about.
At the time,
various US airlines had implemented noise abatement procedures referred to as
“thrust cutback”; using reduced power during the initial climb. This was not
commonly used in Europe but, in the US, aircraft often depart using less thrust
in order to keep the noise levels down as they climbed away from airports. If
there were an engine failure during this time, the power settings would not be
enough to keep that aircraft climbing. There were reasonable concerns that this
added yet another task to a pilot during a time of high workload and, as a
response to this issue, the Automatic Thrust Restoration System was
developed.
In the event
of an engine failure, the Automatic Thrust Restoration System (ATRS) would kick
in, increasing the thrust to the levels that they would have been before the
thrust cutbacks, which would be enough to keep the aircraft from descending. In
the MD-80 type, which has an autothrottle single-clutch configuration, both
thrust levers are advanced to take-off/go-around (TO/GA) thrust level. The
engine throttle levers are automatically moved forward until the thrust of one
engine reaches the engine pressure ratio for going around. This results in the
same effect as pressing the TO/GA button or advancing the thrust levers to the
TO/GA position. This system does exactly what is needed for an engine failure
after take-off: it moves the throttle lever forward to ensure that the good
engine can maintain the climb, while having no effect on the failed engine.
In the MD-81,
the criteria for arming the Automatic Thrust Restoration System are as follows:
- The Flight Director
pitch axis is set for takeoff (the aircraft is climbing)
- The aircraft’s height
above the ground is more than 350 feet (let’s not mess with a plane too
close to the ground)
- The Engine Pressure
Ratio of the engines is below the go-around thrust Engine Pressure Ratio
(insufficient power being delivered for take-off/go-around)
As it
happens, SAS didn’t use thrust cutback for noise abatement and so had no
interest in Automatic Thrust Restoration. It was included as standard in every
MD-81 but the SAS operational documentation had no reference to it and there
seemed to be no understanding of the system at any level of SAS.
The system
was originally developed for use in special procedures not applied by SAS, but
a careful study of the manuals should have led SAS noting the system and
training its pilots in its function.
But, from an
SAS point of view, the initial climb would already happen at take-off/go-around
power and so the ATRS would not kick in even if there was an engine failure.
Although it was included in the MD-81 operational information, at no point was
it mentioned to airlines who weren’t using the thrust cutback procedures. The
fact is that in the almost ten years since the system had been certified, no
one thought of the possibility that an engine stall might be affected by the
increased fuel flow to both engines of the MD-80 type, thus continuing the
stall.
Going back to
that morning over Gottröra, the pilot responded to the right engine surge
correctly, by pulling the right engine throttle lever back by 10%. However, as
they climbed through 350 feet, the three criteria for Automatic Thrust
Restoration had been met and, when the captain released the throttle lever, the
throttle increased again. The right engine continued to surge. A “discreet
indication” on the instrument panel showed that the throttle setting had been
increased automatically. Neither pilot saw it.
About 22
seconds after the first engine surge, the first officer made an inquisitive
sound, apparently asking the captain about the emergency/malfunction checklist.
He took it out but didn’t have a chance to start working through it.
Engine surges
are not unusual but they can rapidly lead to further damage, so the critical
action here is to stop the surges. But engine surging during take-off was not
mentioned in the FAA Approved Flight Manual. There were no memory items in
regards to responding to engine surging in regards to the checklists by the
manufacturer or SAS. The situation was not trained for during type training or
covered in the simulator.
As the crew
had no time to make it through the emergency/malfunction checklist, each
section of which contained at least one or two actions, the captain presumably
didn’t know or think to continue the initial throttle-back on the right engine,
although the MD-81 was still jerking and vibrating. As the engine was still
stalling, he should have been looking to shut it down. The report mentions that
perhaps the captain was even thinking about the British Midland flight 92
accident known as the Kegworth air disaster (two years earlier), in which the
flight crew shut down the wrong engine during an engine malfunction and crashed
into the motorway. Certainly at the time, as a direct result of the Kegworth
disaster, pilots had been warned not to do anything in haste. The
Automatic Thrust Restoration System continued to increase the throttle for both
engines as the aircraft continued the climb.
Meanwhile, in
the back of a cabin was a pilot travelling privately who recognised the
sounds. He approached a cabin crew member in the cabin rear jump seat to
tell her that the right engine was surging. She tried to use the intercom to
alert the captain about this but couldn’t get through — he was, of course,
already trying to deal with the situation and didn’t have time to chat about
it. She passed the message to the Senior Cabin Crew Member who went to the
cockpit to inform the captain that the right engine was surging.
A uniformed
SAS captain was seated in 2C. After hearing multiple surges, he rushed to the
cockpit to see if he could be of any help. He wrote about the incident for
AeroSafetyWorld in 2012.
About 25
seconds after rotation, I heard an engine surge, an appalling sound similar to
a cannon firing. I counted four or five more surges and started to get
worried.
Looking
through the open cockpit door, I saw a lot of warnings on the overhead
annunciation panel but had the impression that nothing was happening between
the two pilots… I also had the feeling that the passengers were looking at me,
wondering why I was sitting there, doing nothing.
The first
officer had handed me the emergency checklist when I entered the cockpit. He
had begun to look for the procedure for engine surge but could not readily find
it because it was so far back in the book.
Thirty
seconds after that first surge, the right engine banged again and then failed
completely. At this stage, they needed to declare an emergency and return
to the airport on the working engine. Thrust loss in one engine should not,
under normal circumstances, affect the other engine.
Just a few
seconds after the right engine failed, the left engine surged.
The Automatic
Thrust Restoration had been steadily increasing the throttle, resulting in more
surges with increased intensity.
From the
report:
It was a
serious deficiency in flight safety that the pilots lacked knowledge of ATR and
its function. ATR is activated without special indication and in such a way
that it can escape the pilots’ notice. Increased throttle on both engines now
took place without the pilots’ knowing.
The left
engine failed almost immediately.
The ice
ingested into the right engine damaged the fan blades at the tips, while the
left engine fan blades had their greatest damage nearer the centre, which is
why the surging started later on the left engine. Once the left engine started
surging, it surged with greater force, because the engine was working at higher
power, which is why the engine broke up after only 14 seconds.
Both engines
were subjected to the same treatment and thus both engines failed.
The initial
damage was not so extensive that the engines would have failed: the right
engine could have continued to provide reduced thrust and if the original power
had been maintained, the left engine might not have surged at all. The aircraft
could have then returned to the airport for landing with both engines operative
(although one with reduced thrust).
Instead, the
MD-81 was now a glider.
The assisting
pilot wrote:
I tossed the
checklist aside because the situation we were in required no checklist. With
both engines out, half the flight instruments blacked out and the aircraft in
clouds, the only things that were required were good airmanship, a hunch about
what the landing configuration should be, and of course, some luck.
It may seem
odd that the checklist was so readily dismissed by the pilots but, in this
case, the checklist was not very helpful. There’s no simulator or other
training to practise dealing with an engine surge. When the situation was recreated
in a simulator, investigators found that getting to the first action in the
checklist took the same amount of time that had taken place between the start
of the surging and both engines breaking up. It happens too fast for the
checklist to be of any use.
For the same
reason, it was pointless for the pilot in the back to try to relay a message
via the cabin crew. The crew member’s call to the cockpit, which went
unanswered, was just ten seconds before the engines failed.
Spread over
two posts like this, I worry that it’s hard to imagine how quickly
everything happened. At this point, the aircraft had been in flight for
only 78 seconds.
The crew
never made a distress call but instead prepared for an emergency landing. At
around 1,400 feet above the ground, while still in cloud and travelling at
about 165 knots, the assisting pilot started gently extending the flaps. As
they reached 1,100 feet, the captain said “Flaps…” and the assisting pilot
responded with “Yes, we have flaps, we have flaps, look straight ahead, look
straight ahead!” The flaps were fully extended as they reached 1,000 feet above
the ground, before the assisting pilot finished his sentence.
The assisting
pilot explained why he kept repeating his instruction.
I told the
captain, who was flying manually, to look straight ahead. I repeated that at
least 20 times during the rest of the flight. Why? Flying a 50,000 kg aircraft
is a full-time job, especially when you don’t have any engine power. I wanted
the captain to do nothing else but fly the aircraft with exact control of speed
and attitude.
The MD-81
broke free of the cloud at around 900 feet above the ground. The captain
saw and dismissed a large field to the right as being too far for them to
reach. He chose another field in the direction of flight, correcting his
heading by about 25° to avoid a populated area which was on his approach
path. He glided the aircraft in a gentle left turn until he was heading
north. The first officer contacted Stockholm control that they had engine
troubles and needed to return to the airport. The air traffic controller
instructed them to make a right turn to bring the aircraft back for landing on
runway 01. However, the captain continued the northerly glide and simply called
out one simple instruction.
Prepare for
on ground emergency.
Procedure was
that one minute before an emergency landing, the captain should turn the
“fasten seat belts” signs on and off, the signal for “brace for impact”. The
captain didn’t do this, instead calling “Prepare for on ground emergency”
repeatedly. But it worked. The assisting pilot repeated his words. Cabin crew
at the front of the aircraft and the passengers in the first rows heard the
call. The senior cabin crew member passed on the announcement using the
loudspeaker system, asking passengers to keep their seat belts fastened and to
keep calm. Twenty seconds before impact, the senior cabin crew member called
out a final instruction: Bend down, hold your knees. The rest of the cabin crew
repeated the instruction in English and in Swedish. Most of the passengers
followed the instructions and adopted the brace position, which is one reason
why there were so few injuries.
The first
officer called out, “Shall we get the wheels down?” The assisting pilot
answered with “Yes, gear down, gear down.”
Eight
seconds later, 200 feet above the ground, the first officer called Stockholm
control.
Stockholm, SK
751, we are crashing to the ground now.
As the
landing gear extended and locked, the aircraft crashed into the trees
travelling at a speed of 121 knots. Most of the right wing was torn off,
forcing the aircraft into a right bank. The path of broken trees was 125
metres long (400 feet). The tail of the aircraft struck the ground first then
the fuselage broke into three pieces on impact. 3,600 litres of aviation fuel
poured out of the right wing tank over the trees. The same amount again spilt
from the left wing at the point of impact.
The overhead
bins opened and many broke off their mountings. Hand baggage fell out of the
bins onto passengers and blocked access to one of the emergency exits. Another
emergency exit was blocked by the galley oven and stowed items. A third was
damaged on impact and would not open.
The assisting
pilot wrote:
When I saw
the trees starting to hammer the aircraft, I had rushed from the cockpit and
braced myself against the forward cabin wall, knowing that I did not have the
time to return to my seat, fasten the seat belt and brace for impact. I felt
the aircraft bank right as I left the cockpit and reached the wall, which was
carpeted and relatively soft, just as the aircraft hit the ground. I was
knocked unconscious.
The impact
forces in the forward part of the aircraft reached +30 g (that is, 30 times
standard gravitational acceleration). It is unbelievable that so many
passengers survived relatively unharmed. I was unconscious for approximately 20
minutes. My left shoulder must have taken most of the impact, because it was
dislocated.
The captain
dragged me to the forward cabin door, where I was taken care of by some
passengers. The slide did not inflate when the crew opened the door because the
distance to the ground was too small. Later, the crew removed the slide and
inflated it. I sat on that slide for a long time, maybe an hour. It was cold,
my shoulder hurt, and I had only one shoe.
The
passengers evacuated through the remaining emergency exits and the openings
left by the broken fuselage.
Meanwhile,
back at Stockholm/Arlanda, Air Traffic Control had raised the alarm for Risk of
accident at 08:50, about a minute before impact. When radar contact
was lost, they updated this to Accident or presumed accident at unknown location.
About 15 minutes later, a passenger phoned from a nearby cottage and was able
to pass on a location.
As I said at
the start, I’m not a fan of good piloting being described as a miracle,
with the implication that the whole thing was in the hand of fate. But in this
case, the good piloting and strong CRM was supported by a number of favourable
factors. There was a good location for an emergency landing directly ahead and
within reach of the descending aircraft, which had had slowed to a suitable
speed for landing, possibly helped by the landing gear snapping off as they
flew through the trees. The way the fuselage broke up meant that there was an
easy means to evacuate the aircraft, which was important as only five of the
eight emergency exits could be used. There was no fire even though the aircraft
was carrying enough fuel for the full flight and the wing tanks broke open on
impact, spreading fuel everywhere.
However, the
passengers were left to wait outdoors in the chilly December weather for quite
some time. When the duty fire engineer arrived, he found that only a few people
were injured. He knew that a number of helicopters, ambulances and buses were
on their way and so he did not order heated tents on the accident site and he
did not set up a management team, presuming that the would clear the crash site
quickly. The first inventory of the injured was completed in about an hour
and the most seriously injured were taken or prepared for transport.
There were a
number of communication issues which led to the buses for transporting the
passengers remaining by the church rather than continuing to the accident location.
The police took great pains to register everyone on site, checking them against
the passenger list to ensure that no one was missing. However, they did not get
the passenger list until 14:00, over half an hour hours after the
accident (see Leif’s comment below). Some of the uninjured and slightly injured
passengers had made their way to the cottage, which meant that the police were
unable to account for all the passengers and required additional resources to
search for those who were presumed missing.
In the end,
everyone was accounted for and, despite the crash and the cold and the wait, it
was clear that something close to the miraculous had happened: only one member
of the crew and eleven passengers were injured. Of those, only one was serious.
3.2 Causes of the accident
The accident
was caused by SAS’ instructions and routines being inadequate to ensure that
clear ice was removed from the wings of the aircraft prior to takeoff. Hence
the aircraft took off with clear ice on the wings. In connection with liftoff,
the clear ice loosened and was ingested by the engines. The ice caused damage
to the engine fan stages, which led to engine surges. The surges destroyed the
engines.
Contributory Causes
The pilots
were not trained to identify and eliminate engine surging.
ATR – which
was unknown within SAS – was activated and increased the engine power without
the pilots’ knowledge.
I find it
interesting that there’s seemingly no emphasis made on the design of the
aircraft, which led to the ingestion of clear ice in a way not seen in other
aircraft. The issue was clear, however. Just a week after the
accident, the FAA made it obligatory to install four warning triangles
with indication tufts on the upper surface of the wings of all MD-80 aircraft. Staff
at Stockholm/Arlanda were retrained and a stronger emphasis put on pilot
training to deal with clear ice and engine surges, including amending the
checklist to include memory items. And the manuals were redesigned to ensure
that pilots were aware of the Auto Throttle System and the Automatic Thrust
Restoration and, more importantly, knew how to disable it in the case of engine
surging.
Still, a
happy ending and a lesson learned. Can’t ask for much better than that.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Hi Dave,
Feliz Christmas!!
Attached is this year’s version of my annual Christmas poem. Can you forward this to all of your minions and devotees, as well as your friends, colleagues and cronies? I’ve included it as a separate document, so that it can easily be printed and pasted it on a refrigerator, or even copied for anyone else to have forever.
Also, it’s a part of the text below, in case folks just can’t wait to print it.
I hope it makes you all smile.
Live, love, laugh….
Jeff
Christmas 2020
I look back at the last twelve months; it’s been a crazy year,
With times of peace that coexist with times of stress and fear.
Our lives have all been touched by the fearsome Covid virus
And for the nearby future, we’re so hopeful and desirous!
Takeout meals and “distancing” are currently the norm,
And face masks do far more for us, than keeping noses warm.
We may watch, with interest, the paths of Trump and Biden,
But politics aside, our smiles now are poised to widen.
As you contemplate these lines, written in December,
Let’s identify, together, good things to remember,
From the beauty of a redbird against a snow-clad tree,
To a simple prayer of gratitude, upon a bended knee.
The piney smell of fresh, cut wreathes is often in the air,
Vying with the scent of cookies, wafting here and there.
Christmas lights against the night look like colored polka-dots,
Reflected in bright, glowing eyes from seniors down to tots.
But while it’s true we’ve stayed inside considerably more,
Was this better served than always rushing out the door?
Maybe now the chance was there to really learn to cook,
And to exercise more often, or even write a book!
We’ve taken things for granted, perhaps for far too long,
But now, upon reflection, we can come out feeling strong.
To cherish, from the ones we love, each warm embrace and touch,
While saying lots of “thank yous”…‘cause we really have so much.
And so, my friends, this pensive poem is just about to end,
A promising new year is waiting, just around the bend.
So, with relief, we look ahead to twenty-twenty-one:
May it be full of Delta trips, with health and joy and fun!
Jeff deltajeff8@gmail.com
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