Wait to Weight & Balance – Lessons from a PC-12 Loss of Control
On take off, pitch control of a Pilatus PC-12 was lost resulting in a series of pitch oscillations and stall warnings. Fortuitously the pilot was able to abort the take off with only damage to one main wheel. The incident could have been avoided if a more rigorous approach had been taken to aircraft loading.
The US National Transportation Safety Board (NTSB) recently reported on this incident. It involved PC-12 N617BG, operated on a Part 135 commercial on-demand passenger flight by operated as a commercial on-demand passenger flight by FlighTime Business Jets, LLC from Austin-Bergstrom International Airport (AUS), Texas with 9 persons on board on 12 September 2013.
The pilot stated:
At rotation speed I smoothly and steadily rotated to establish a positive rate of climb to Vx (120 knots). As the aircraft accelerated to 95 knots the airspeed stagnated and a positive rate of climb was not possible. Simultaneously, at 95 knots, the aural STALL WARNING activated accompanied by the STICK SHAKER. This was immediately followed by the STICK PUSHER violently pitching the nose down at the runway. I was able to override the STICK PUSHER to avoid a nose wheel impact on the runway. When I leveled the aircraft at about 20-30 feet AGL, the unaccelerated airspeed was still in the 95 knot range and again the aural STALL WARNING and STICK SHAKER activated. This again was followed by an immediate and violent nose pitch down caused by the STICK PUSHER. I repeated a recovery to level flight and avoided runway contact. The scenario repeated itself once again and the airspeed continued to appear to be stagnant. Again at about 95 knots the aural STALL WARNING and STICK SHAKER activated which was immediately followed by a STICK PUSHER violent downward pitch. Again I recovered from the unusual attitude and avoided runway contact. After this recovery I was able to establish wings level and aborted the takeoff.
The company’s FAA Operations Specifications stated that ‘only actual weights’ be used when determining the aircraft weight and balance.
Irrespective of regulation, the use of actual weights for smaller aircraft is good practice recognised in industry standards:
- The International Association of Oil & Gas Producers (IOGP), formerly better known as OGP, recommends the use of actual weights for aeroplanes below 5,700kg and helicopters in para 9.4.1 of their Aviation Management Guidelines (Publication 390).
- The Flight Safety Foundation’s award winning Basic Aviation Risk Standard (BARS) for contracted air operations requires the use of actual weights for aircraft of less than 30 passengers (Control 6.1).
The NTSB explain that:
The pilot’s weight and center of gravity graphical plot for the incident flight did not take into account carry-on items/baggage [and] showed a CG of about 239 inches and a weight of 10,369 lbs.
However the FAA reported to the NTSB that:
…about 490 lbs of carry-on items were not included in the weight and balance for the incident flight. The items consisted of a small ice chest and food that weighed about 60 lbs and four ice chests and boxes of food that weighed about 430 lbs. The actual passenger weights obtained for the flight was 2,031 lbs, which was obtained from passenger interviews. A weight and center of gravity plot showed that the incident flight was about 4 inches aft of the aft center gravity limit and about 100 lbs above the maximum ramp weight of the airplane.
Further the NTSB report:
Passengers stated that their weights were not verified before the flight and there were several coolers aboard that they had to climb over to get to their seats. They were not asked by the pilot or operator the weight of cargo/carry-on items, which included coolers they had brought for the flight. The coolers were not tied down for the flight. Passengers stated that they did not receive a passenger briefing for the flight.
Three of the listed passengers were replaced and the Trip Sheet was not updated to reflect the replacement.
The carriage of unrestrained items in the cabin is also a significant risk in the event of a accident, both as causes of injury and of evacuation obstruction. Again this is a feature of FSF BARS (Control 6.2), as is a passenger briefing (Control 6.6), also discussed by IOGP (AMG para 9.5) and accurate manifesting (Control 6.4 and para 9.3.3).
The FSF BARS and the IOGP AMG are however silent on the quantity of food and beverage necessary for a flight! As the destination, Lubbock (LBB), was about 90 minutes away, 490 lbs of ice boxes for 9 people may seem rather excessive! In practice as the flight was scheduled to depart AUS at 1515 to arrive at LBB at 1651 and return from LBB at 2145 to land at AUS at 2315, one might suspect that the party were travelling to watch an evening sports event.
One more serious observation we make is that while the pilot was qualified on ‘A-310, AVR-146, B-737, B-757, B-767, B-777, BAE-146, DC-9, LR-JET’ they had only converted to the PC-12 a few weeks prior. Acting a single pilot on PC-12 introduces duties that are not normally routinely practiced by airline pilots.
The aircraft was fitted with a Lightweight Data Recorder (LDR), something that Aerossurance has commented on previously after a C208 Caravan accident, an AS350 loss of control incident and the creation on an EASA Rule Making Team. However:
The recording indicated that it contained approximately 25 hours and 35 minutes of flight data. A new file was generated for each power cycle. The LDR also contained 2 hours of cockpit audio; however, the incident flight was overwritten and not available for evaluation.
Pilatus were however able to analyse other recorded data for NTB and their report is in the NTSB Public Docket.
The NTSD determined the probable cause(s) to be:
The pilot’s improper weight and balance calculations, which resulted in the airplane exceeding its weight and center-of-gravity limits and led to a loss of pitch control during takeoff, and the operator’s failure to obtain required weight information and to ensure that the flight was properly loaded.
Australian Transport Safety Bureau (ATSB) report Aircraft loading occurrences July 2003 to June 2010
UPDATE 5 May 2015: Loading issues also featured in this Canadian accident: Culture + Non Compliance + Mechanical Failures = DC3 Accident
UPDATE 15 July 2015: Inadequately Secured Cargo Caused B747F Crash at Bagram, Afghanistan
UPDATE 21 October 2015: Misloading Caused Fatal 2013 DHC-3 Accident
UPDATE 12 January 2016: The Passengers Who Caused a 737 Tail Strike: Ground Handling Lessons
UPDATE 24 October 2016: Execuflight Hawker 700 N237WR Akron Accident: Casual Compliance A disturbing accident after an unstabilised approach that begs serious questions of the operator’s procedures and culture.
UPDATE 11 August 2017: Deadly Combination of Misloading and a Somatogravic Illusion: Alaskan Otter A night departure of a Otter in Alaska into a ‘back hole’ when outside of the weight and CG limits resulted in spatial disorientation, a stall and LOC-I.
UPDATE 9 February 2018: The Irish AAIU explain how during preparations for departure from Dublin of ATR72-212 EI-FAV on 23 July 2015 the passenger baggage was placed in the aft aircraft baggage hold instead of the forward baggage hold. “The aircraft departed with the Centre of Gravity outside approved loading limits. The aircraft subsequently landed at its destination where the loading error was discovered”.
UPDATE 13 October 2018: Low Viz Helicopter Accident, Alaska, also with a loading aspect.