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Use of Erroneous Parameters at Take-Off

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Article Information
Category: Runway Excursion Runway Excursion
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary

Description

The use of erroneous take-off parameters (i.e., thrust and speeds), usually as a result of using incorrect values for take off weight in performance calculations, can result in early rotation with tail strike, loss of control when airborne, or overrun as a result of failure to get airborne.

Currently, training also emphasises risk mitigations by flight crews every time they conduct, or know they must not conduct, reduced-thrust take-offs. In this maneuver, flight crews opt to utilise up to 25% less thrust than many jet engines are capable of producing under the existing conditions of temperature and pressure altitude. Aircraft operating manual (AOM) limitations, the runway specific criteria of length, altitude and obstacles factored against the actual aircraft weight and existing environmental conditions allow the calculation of the actual amount of thrust necessary to meet regulatory requirements for safe takeoff.

One 2017 serious incident noted in this article details the flight crew’s unawareness that they actually were conducting — because of take-off–parameter oversights — an assumed-temperature, reduced-thrust take-off as opposed to a required full-thrust take-off (see Accidents and Serious Incidents). The final investigation report also cited their inadequate response to the pre-take-off alert message “VERIFY TAKEOFF SPEEDS” on their flight displays.

Identifying Common Causes

In 2007, following the investigation of two serious incidents involving tail strikes that had occurred at Paris, Charles de Gaull Airport (LFPG), a study entitled "USE OF ERRONEOUS PARAMETERS AT TAKEOFF" was conducted by the Applied Anthropology Laboratory (LAA) at the request of Le Bureau d'Enquêtes et d'Analyses (BEA) and the French Civil Aviation Authority (DGAC).

Various investigation bodies, airlines and manufacturers were consulted in the course of the study because several other accidents, serious incidents and incidents of the same type have occurred around the world during recent years. These generally involved new generation aircraft. The causal factors included flight crew errors of varying degrees of significance when they entered take-off parameters; the errors were not detected by the crews.

The most serious event occurred in 2004 and involved the destruction of a B747-200 Cargo on takeoff at Halifax. All crew members were killed and the aircraft was destroyed. Other errors compiled in the LAA researchers’ database included those of various airlines and various types of large commercial transport aircraft, intentionally limited in scope to those manufactured by Airbus and Boeing.

As noted, serious incidents and incidents arising from data-entry errors of the same type have continued since the study. They have involved latest-generation large and medium-sized aircraft, such as Embraer 190, in addigtion to types from the manufacturers mentioned.

The complete text of the study is accessible from (See: Further Reading).

Conclusion of the Study

In conclusion, the research identified the following problematic issues:

  • The variety of events shows that the problem of determining and using takeoff parameters is independent of the operating airline, aircraft type, equipment and method used,
  • Errors relating to takeoff data are frequent. They are generally detected by application of airline operating modes or by personal methods such as mental calculation,
  • Studied cases reveal that failures correspond to the "calculation of takeoff parameters" and "input of speeds into the FMS" functions, but do not correspond to errors in the "weight input into the FMS" function,
  • In several cases, the Zero Fuel Weight (ZFW) was entered instead of the Take-off Weight (TOW) into the performance calculator,
  • Half of the crews who responded to the survey carried out in one of the participating airlines had experienced errors in parameters or configuration at takeoff, some of which involved the weight input into the FMS,
  • Pilots' knowledge of the order of magnitude of these parameter values, determined by empirical methods, is the most frequently cited strategy used to avoid significant errors,
  • Input of the weight used in parameter calculation, in whatever medium it may be (by ACARS, in a computer, manually), is one of the determining steps in the process of takeoff preparation. It is this, by affecting both the thrust and the speeds, that determines takeoff safety,
  • The real-time availability of final weight information shortly before departure requires the crew to perform a large number of tasks, inputs and parameter displays under strong time pressure,
  • Checks on the "takeoff parameter calculation" function can be shown to be ineffective because they consist of verifying the input of the value but not the accuracy of the value itself,
  • In the same way, the check of data featuring on several media often proves to be ineffective. It is often limited to item by item comparisons. If the item is wrong, the check is correct but inadequate because it doesn't cover overall consistency. In particular, there is no comparison between values for takeoff weight given in the final loadsheet, on the takeoff paper or electronic "card" and in the FMS,
  • The reference speed values suggested by some FMS can be easily changed. They do not enable routine detection of prior calculation errors,
  • Studied FMS allow insertion of weight and speed values that are inconsistent or outside the operational limits of the aircraft concerned. Some accept an omission to enter speeds without the crew being alerted,
  • The weight values manipulated by crews before the flight can appear, depending on the documents or software, under various names or acronyms and in different units and formats for the same data, which makes them too difficult to memorise,
  • Time pressure and task interruptions are frequently cited in surveys as common factors contributing to errors. The observations showed that the crews' work load increases as the departure time approaches and that the normal operation actions of the captain were all the more disrupted,
  • During the takeoff run, the possible decision to reject takeoff based on an erroneous V1 no longer guarantees safety margins,
  • On cockpit display screens of the PFD-type (Primary Flight Display), the marker representing Vr is not displayed at low speed. Further, it can be difficult to distinguish it from the marker representing V1, especially when the two values are similar.
  • In several cases, crews perceived abnormal airplane behaviour during takeoff. Some took off “normally”, i.e. no abnormal behaviour counter strategy was applied. Others were able to adopt different strategies: stopping takeoff, increasing thrust, delayed rotation.

Risk Management

The following risk factors were notede in reports by EUROCONTROL, Singapore civil aviation authorities and aviation safety experts at other organisations during since 2010:

  • Inadvertent reduced-thrust take-off — According to a SKYbrary article, “Use of erroneous parameters at take-off may lead to severe operational consequences whenever a reduced-thrust take-off is conducted. A reduced thrust takeoff will result in a slower acceleration on the runway, a longer takeoff roll and a reduced initial climb rate.

“The principal risks associated with a reduced thrust takeoff are the potential of miscalculating either or both of the derate or assumed temperature values and the possibility of entering incorrect values into the aircraft flight management system (FMS). Either of these errors could result in the engines producing insufficient thrust to safely execute the takeoff.

"[Among defences to these risks,] when derate or assumed temperature calculations are made by the pilots utilizing either manual or electronic means, each of the pilots should make the calculations independently and then compare the results. Differences must be reconciled. Likewise, all FMS entries should be crosschecked by both pilots for accuracy.”

  • Findings of the 2017 serious incident report — This report, issued by Singapore’s national aviation authorities in 2019 (see Accidents and Serious Incidents), included several conclusions about the causal factors and defences that could have been used by this flight crew and others. The report said, “The aircraft took off with [an inadvertent] reduced thrust take-off of 90.4% as determined by the [flight management computer (FMC)] using an assumed temperature of 67°C.

“The thrust setting was significantly below that required for the conditions of the day and the runway length available. The assumed temperature of 67°C was somehow inadvertently introduced into the FMC. The flight crew could have noticed the discrepancies between the results of the [Boeing Onboard Performance Tool (OPT)] and FMC had they followed both the operator’s and the aircraft manufacturer’s procedures. The FMC calculations of V-speeds and N1 setting did not take into account the runway length available, unlike the OPT calculations.”

Accidents & Incidents

Events in the SKYbrary database which include Pre Flight Data Input Error as a contributory factor:

  • A319, Nice France, 2019 (On 29 August 2019, an Airbus A319 crew used more runway than expected during a reduced thrust takeoff from Nice, although not enough to justify increasing thrust. It was subsequently found that an identical error made by both pilots when independently calculating takeoff performance data for the most limiting runway intersection had resulted in use of data for a less limiting intersection than the one eventually used. The Investigation concluded that the only guaranteed way to avoid such an error would be an automatic cross check, a system upgrade which was not possible on the particular aircraft involved.)
  • A320, Porto Portugal, 2013 (On 1 October 2013, an Airbus A320 took off from a runway intersection at Porto which provided 1900 metres TORA using take off thrust that had been calculated for the full runway length of 3480 metres TORA. It became airborne 350 metres prior to the end of the runway but the subsequent Investigation concluded that it would not have been able to safely reject the take-off or continue it, had an engine failed at high speed. The event was attributed to distraction and the inappropriate formulation of the operating airline's procedures for the pre take-off phase of flight.)
  • A321, Glasgow UK, 2019 (On 24 November 2019, as an Airbus A321 taking off from the 2665 metre-long runway 05 at Glasgow approached the calculated V1 with the flex thrust they had set, the aircraft was not accelerating as expected and they applied TOGA thrust. This resulted in the aircraft becoming airborne with less than 400 metres of runway remaining. The Investigation confirmed what the crew had subsequently discovered for themselves - that they had both made an identical error in their independent EFB performance calculations which the subsequent standard procedures and checks had not detected. The operator is reviewing its related checking procedures.)
  • A321, Manchester UK, 2011 (1) (On 29 April 2011, an Airbus A321-200 being operated by Thomas Cook Airlines on a passenger service from Manchester UK to Iraklion, Greece took off in day VMC but failed to establish a climb at the expected speed until the aircraft pitch attitude was reduced below that prescribed for the aircraft weight which had been entered into the FMS. No abnormal manoeuvres occurred and none of the 231 occupants were injured.)
  • A332, Montego Bay Jamaica, 2008 (On 28 October 2008, an Airbus A330-200 could not be rotated for liftoff whist making a night takeoff from Montego Bay until the Captain had increased the reduced thrust set to TOGA, after which the aircraft became airborne prior to the end of the runway and climbed away normally. The Investigation found that the takeoff performance data used had been calculated for the flight by Company Despatch and the fact that it had been based on a takeoff weight which was 90 tonnes below the actual take off weight had not been noticed by any of the flight crew.)

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Continuing the data entry theme, the following events in the SKYbrary database include Data use error as a contributory factor:

  • A306, Paris CDG France, 1997 (On 30 July 1997, an Airbus A300-600 being operated by Emirates Airline was departing on a scheduled passenger flight from Paris Charles de Gaulle in daylight when, as the aircraft was accelerating at 40 kts during the take off roll, it pitched up and its tail touched the ground violently. The crew abandoned the takeoff and returned to the parking area. The tail of the aircraft was damaged due to the impact with the runway when the plane pitched up.)
  • A310 / B736, en-route, Southern Norway, 2001 (On 21 February 2001, a level bust 10 nm north of Oslo Airport by a climbing PIA A310 led to loss of separation with an SAS B736 in which response to a TCAS RA by the A310 not being in accordance with its likely activation (descend). The B736 received and correctly actioned a Climb RA.)
  • A310, Vienna Austria, 2000 (On 12 July 2000, a Hapag Lloyd Airbus A310 was unable to retract the landing gear normally after take off from Chania for Hannover. The flight was continued towards the intended destination but the selection of an en route diversion due to higher fuel burn was misjudged and useable fuel was completely exhausted just prior to an intended landing at Vienna. The aeroplane sustained significant damage as it touched down unpowered inside the aerodrome perimeter but there were no injuries to the occupants and only minor injuries to a small number of them during the subsequent emergency evacuation.)
  • A310, vicinity Birmingham UK, 2006 (On 24 November 2006, an A310 descended significantly below cleared altitude during a radar vectored approach positioning, as a result of the flight crew's failure to set the QNH, which was unusually low.)
  • A319 / A321, en-route, west north west of Geneva, Switzerland 2011 (On 6 August 2011 an Easyjet Airbus A319 on which First Officer Line Training was in progress exceeded its cleared level during the climb after a different level to that correctly read back was set on the FMS. As a result, it came into conflict with an Alitalia A321 and this was resolved by responses to coordinated TCAS RAs. STCA alerts did not enable ATC resolution of the conflict and it was concluded that a lack of ATC capability to receive Mode S EHS DAPs - since rectified - was a contributory factor to the outcome.)

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