|
![Skip all menus (access key: 2)](/web/20060212031212im_/https://www.tc.gc.ca/images/18px.gif) |
Controlled Flight Into Terrain (CFIT) at Night
![Aircraft collided with trees and terrain](/web/20060212031212im_/https://www.tc.gc.ca/CivilAviation/SystemSafety/Newsletters/tp185/4-99/images/131.jpg)
On January 15, 1998, a Piper PA-31-350 Chieftain was on a passenger flight
from Edmonton to High Level, Rainbow Lake, Edmonton and Calgary, Alberta. Following
an uneventful flight to Rainbow Lake, the aircraft departed in darkness at 19:35
Mountain standard time on an instrument flight rules (IFR) flight to Edmonton. Shortly
after takeoff from Runway 27 the aircraft collided with trees and terrain
approximately 3000 ft. west of the departure end of the runway. The
9 occupants sustained minor injuries, and the aircraft was substantially damaged.
This synopsis is based on the Transportation Safety Board of Canada (TSB) Final Report
A98W0009.
The sky was clear with unrestricted visibility and light winds. The ambient
lighting conditions were described as dark, with no moon, little illumination from
the night sky and no lights to the west of the airport. The operator chartered the
Piper PA-31-350 Chieftain and a pilot from another company. The company had flown the
route for the operator in the past; however, the pilot had not previously flown for
that operator. He had been employed as a charter pilot for approximately 6 months,
held a valid airline transport pilot licence (ATPL) and had accumulated 3700 hrs
of flight time, including 93 hrs on Piper PA-31 aircraft and 590 hrs at
night. His background included flight instruction and charter. The majority of his
charter experience was as a single pilot. He had never received formal two-crew flight
training, recurrent ground training or simulator training that emphasized CFIT
prevention strategies.
The operator routinely assigned two pilots to comply with the requests of a number
of regular passengers and to inspire confidence. In accordance with that policy, a
"co-pilot" was part of the flight, but was in fact a customer service
representative, and not a flight-crew member. He assisted with baggage loading,
passenger briefings and so on. He held a commercial pilot licence with an instrument
rating, but did not hold a pilot proficiency check (PPC) for a Piper PA-31. The captain
preferred to operate the aircraft as a single pilot, and the "co-pilot" was
not assigned any formal cockpit duties.
There were no reported mechanical abnormalities with the aircraft. It was fitted
with an approved supplementary device that increased the maximum permissible takeoff
weight from 7000 lb. to 7368 lb. Runway 27 at the Rainbow Lake Airport
is 4500 ft. long, with low-intensity runway edge lights, green threshold and red
end lights and no approach lighting. It slopes uphill, and departures are accomplished
into rising terrain.
Each passenger was permitted to transport a maximum combined weight of 50 lb.
When the total load exceeded the gross weight of the Chieftain on any leg of the
flight, it was the operators policy to remove the second pilot from the flight
before reducing the number of passengers. Neither the chartered company nor the pilot
had been advised of this policy.
The pilot completed a computer-generated flight plan and gross weight calculation,
but there was no evidence that centre-of-gravity (C of G) calculations were performed.
The visual flight rules (VFR) flight plan indicated that there would be a fuel stop in
Peace River on the return leg. However, when the aircraft arrived in High Level, the
pilot was informed that the operator did not normally stop in Peace River for fuel and
preferred that the aircraft not do so in order to ensure that the flight remained on
schedule. The pilot consulted with the "co-pilot" and was advised that one
male passenger had been replaced with a female passenger, that most of the passengers
would be travelling light, and that several of them weighed less than the standard
passenger weight. The pilot amended the flight plan and added fuel to complete a VFR
flight to Rainbow Lake and an IFR flight to Edmonton. A copy of the original
company flight plan indicated that the pilot had originally planned to leave
Rainbow Lake with 504 lb. of fuel.
Calculations completed after the accident indicated that approximately 850 lb.
of fuel were on the aircraft at the time of departure from Rainbow Lake. Weight and
balance calculations using estimated baggage and standard passenger weights indicated
that the aircraft was at approximately 7473 lb. on takeoff from Rainbow Lake, and
that the C of G was near the aft limit. Calculations using passenger self-reported
weights indicated that 7 of the 9 passengers exceeded the standard passenger
weight, that the aircraft was approximately 7683 lb., or about 315 lb. above
the approved gross weight at takeoff, and that the C of G was about 0.35 in. aft
of the aft limit.
The aircraft struck several trees with wings level in an approximate three-degree
descent. It came to rest upright, and the cockpit and cabin sections remained intact;
the occupant survival space was not compromised. The wings-level impact attitude, the
shallow impact angle, the small tree size and the presence of approximately two feet
of snow on the ground had contributed to maintaining the deceleration forces within
the limits of human tolerance. The aircraft was reportedly equipped with a survival
kit, as required by regulation, but investigators did not locate the kit in or near
the aircraft.
Aircraft using Rainbow Lake airport typically take off from Runway 09 during
night departures if the wind conditions permit, as several lights are visible to the
east then. On arrival at Rainbow Lake, the pilot had been advised by the
"co-pilot" of a minor frost heave in Runway 09 near the runway
threshold. To avoid the risk of damaging the nosewheel during takeoff, the pilot
elected to depart on Runway 27.
The pilot selected 10° of flap for takeoff and rotated at 85 kt. indicated
airspeed (IAS). He believed that the aircraft became airborne at 90 kt.
approximately halfway down the runway, and that he had established and maintained a
positive rate of climb. He reported that he was waiting for the aircraft to accelerate
to the "blue line" speed (best single-engine rate of climb) of
107 kt. IAS prior to lifting the flaps when the aircraft struck the trees. The
landing gear and the flaps were in the UP position at impact.
Soon after liftoff, the pilot was confronted with dark, featureless terrain.
Darkness and the absence of external visual clues may induce a false perception of
altitude and attitude. Under acceleration, the combination of gravity and inertial
forces produces a resultant force at an angle aft of the true vertical. This force,
acting on the vestibular system of the human inner ear, can give a false pitch-up
sensation. While the aircraft may be flying straight and level or climbing slightly,
pilots may have a sensation of climbing at a much steeper angle than they actually are.
Without visual input to override the false sensation, the pilot will usually pitch the
aircrafts nose down to correct the perceived steep climb, and inadvertently
descend. This form of spatial disorientation is known as the "false climb"
or somatogravic illusion. The extent, if any, to which somatogravic illusion
contributed to this accident was not determined.
The TSBs analysis focused on the pilots applied IFR/night takeoff
technique, the role and influence of the "co-pilot," the communications
between the chartered company and the operator, the request to change the flight plan,
and the effect of the overweight condition of the aircraft on the departure.
Individually, these factors would likely not have been significant enough to cause an
accident. When combined with dark ambient conditions and an uphill takeoff toward
rising terrain, these factors collectively established a window of opportunity for
an accident to occur.
The pilots night departure technique is considered to be the active failure
in this accident. Night departures in dark conditions require full use of the aircraft
flight instruments, and it is essential that the pilot achieve and maintain a positive
rate of climb. In the absence of outside visual cues, the pilot must rely on the
aircraft instruments to maintain airspeed and attitude and to overcome any false
sensations of climb. The pilot was either relying on outside visual cues during the
initial climb and/or using only a partial instrument panel scan while being influenced
by the false-climb illusion. Pilots can overcome false sensations by flying the
aircraft with reference to the altimeter, vertical speed indicator, attitude indicator
and airspeed indicator, which, in this case, would likely have allowed the pilot to
detect that the aircraft was not in a climb. The appropriate technique would have been
to climb at the aircrafts best rate or best angle-of-climb speed until above all
obstacles rather than become preoccupied with reaching blue line.
The role of the "co-pilot" is somewhat ambiguous, and his presence does
not appear to have contributed to the safety of the flight. Because he was not familiar
to the captain and because he was not delegated flight-crew responsibilities, his
participation during the flight created a situation of crew resource mismanagement. The
co-pilots remarks regarding the weight and flight-plan changes at High Level
appear to have encouraged the captain to cancel the planned fuel stop in Peace River.
The co-pilot did not advise the captain that, if weight was a concern, he could remain
in Rainbow Lake. The co-pilots apparent well-intentioned advice on the frost
heave near the threshold of Runway 09 influenced the captains decision to take
off on Runway 27, which was uphill toward rising terrain and with no lights
visible after departure.
The estimated weight of the aircraft at takeoff, which was approximately
315 lb. above the prescribed increased gross weight, and the C of G, which was
at or beyond the rear limit, would have increased the takeoff distance and reduced
the climb performance of the aircraft. The request to the captain in High Level to
add fuel in order to avoid a stop at Peace River contributed to the aircrafts
being overweight on departure from Rainbow Lake.
Communication between the operator and the chartered company with regard to the
duties of the co-pilot and the weight of the aircraft at departure from Rainbow Lake
were inadequate. Both companies were familiar with Piper PA-31-350 capabilities, and
the weight and balance calculations performed prior to the aircrafts leaving
Edmonton indicated that the trip would have to be accomplished VFR, with a fuel stop
at Peace River, to accommodate the passenger load. Critical information, such as the
option of dropping the co-pilot in the event of an overweight aircraft condition, was
never provided to the chartered company. The pilot, who was the final decision-maker,
was put in the position of having to balance the conflicting objectives of operating
the aircraft within the prescribed weight limits and satisfying the customers
demands. He was relatively inexperienced on Piper PA-31-350 aircraft, having flown
less than 100 hrs on the type, and, because he had not previously flown for the
operator, he was unfamiliar with its daily flight routine.
The TSB determined that the aircraft was inadvertently flown into trees and the
ground in controlled flight and dark ambient conditions during a night departure
because a positive rate of climb was not maintained after takeoff. Factors contributing
to the accident were the pilots concentrating on blue-line speed rather than
maintaining a positive rate of climb, the dark ambient conditions, a departure profile
into rising terrain, an overweight aircraft and crew resource mismanagement.
|