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Long History of Turbulence Recommendations; Most Miss the Target

Thu, Jul 29, 2010 — David Evans

Articles, Featured

Investigation of the 20 July 2010 turbulence incident involving a United Airlines B777 over Missouri has just begun, but already a broader question arises: why haven’t all the National Transportation Safety Board (NTSB) recommendations to combat exposure to turbulence had an effect? People are still thrown about the cabin from turbulence about 5,000 times a year worldwide. Given the sheer size of the U.S. airline industry and the propensity for thunderstorm-related turbulence over the Midwest, at least 2,000 of these 5,000 encounters with turbulence involve domestic mayhem.

Aftermath of an encounter with turbulence.

Aftermath of an encounter with turbulence.

The latest incident involves a United B777 cruising at 34,000 feet, about 60 miles southeast of Kansas City, right into a wall of convective turbulence rising at 50-100 mph. The flight crew apparently made no evasive action (to be explored by NTSB investigators, for sure), and the airplane’s 265 passengers and crew were subjected to what one passenger described as “just a huge up and down.” Four flight attendants and about 20 passengers were injured to the extent that hospitalization was necessary. Fortunately, and unlike past turbulence encounters, there were no deaths. (See Aviation Safety Journal, ‘Turbulence During Flight Injures Scores; After Years of Such Events, Why Do They Continue?’)

The NTSB has been issuing recommendations to counter turbulence encounters and injuries since the early 1970s. Either the recommendations are not relevant to the real dynamics of the problem, the Federal Aviation Administration (FAA) has not responded effectively, or some combination of both factors must be at fault.

Here is a roll-up of every NTSB turbulence-related recommendations for the last 30+ years and current status (general perusal sufficient; observations/conclusions about turbulence during the cruise phase of flight follows the table):

Turbulence-Related Recommendations & Their DispositionRed: Closed — Unacceptable ActionGreen: Closed — Acceptable Action

Orange: Open – Awaiting Final Disposition

Underlined recommendations deal with en route turbulence

Year Issued/Recommendation No. NTSB Recommendation FAA Response Year of Latest NTSB Classification & Judgment
1972A-72-008 Examine the feasibility of developing a severe weather avoidance system, at least on an experimental basis at selected locations. Severe weather avoidance plan published as FAA Order 7110.47. 1975CLOSED – Acceptable Action
1972A-72-076 Reevaluate wake turbulence separation criteria behind heavy jet aircraft. Advisory Circular (AC) 90-23B issued on wake vortex avoidance procedures. 1973CLOSED – Acceptable Action
1972A-72-215 Include wake turbulence warnings on ATIS [Automated Terminal Information System] broadcasts. ATIS broadcasts are not appropriate for wake turbulence information. 1974CLOSED – Unacceptable Action
1972A-72-218 Develop methods for tower controllers to aid pilots of flights in the traffic pattern to maintain adequate separation to avoid wake turbulence encounters. The AC on Wake Turbulence is quite descriptive, hence, any pilot who studies this information can adopt operating procedures to avoid wake turbulence encounters. 1974CLOSED – Acceptable Action
1973A-73-045 Revise Santa Ynez, CA, airport approach plates to warn pilots of areas where turbulence and downdrafts occur. Approach to Santa Ynez airport is considered sound but a caution note will be added on the approach charts. 1974CLOSED – Acceptable Action
1973A-73-002 Require galleys, lavatories and lavatory waiting areas to be designed so that persons using these areas will not likely suffer serious injury in turbulence. We consider the protection of persons is adequately addressed in FAR 25.785(A), (D) and (E). A change to section (B) will require latches to prevent inadvertent opening of doors in the passenger and crew cabin. 1982CLOSED – Acceptable Alternate Action
1974A-74-013 Install radar at airports capable of locating severe weather and use the information to vector airplanes around it. The FAA contracted for delivery of 47 TDWR [terminal doppler weather radar] and plans to buy an additional 104 systems. 1990CLOSED – Acceptable Action
1977A-77-063 Expedite the development and implementation of a weather subsystem for both en route and terminal areas that provides a real time display of turbulence. Transmit this info to pilots via the controller or by data link. The AAS [advanced automation system] will provide a fully integrated display of traffic and weather. Data link will be used to advise pilots. The FAA has met the intent of the recommendation. 1990CLOSED – Acceptable Action
1981A-81-103 The National Ocean & Atmospherics Administration (NOAA) should define the relationship between clear air turbulence (CAT) and upper fronts & utilize the information to improve forecast. The relationship between CAT and “upper fronts” has been found to be of negligible value. Need improved technology. 1982Closed – No Longer Applicable
1982A-82-098 Issue a bulletin to ensure the following safe operations procedures are followed: (1) the pilots brief flight attendants on expected turbulence, (2) PA announcements of turbulence be made to warn flight attendants and passengers to get in their seats and buckle up. FAA issued Air Carrier Operations Bulletin (ACOB) No. 1-76-19, which complies with the intent of the safety recommendation [although the ACOB does not require compliance, which is also the problem with ACs]. 1985CLOSED – Acceptable Action
1984A-84-108 NOAA forecasters should be alert for jet streams colliding with thunderstorms and issue warnings. Guidelines for more appropriate forecast techniques should be developed in the not-too-distant future. 2002CLOSED – Acceptable Action
1986A-86-076 Staff center weather service units (CWSU) constantly to provide appropriate information about wind shear, icing, and turbulence. FAA will evaluate to see if personnel costs are feasible. Will be notified when CWSU meteorologists leave the operations area. 1994CLOSED – Acceptable Alternate Action
1990A-90-076 Impose a 3-minute delay on small aircraft departing behind a large aircraft to minimize threat of wake turbulence. The 3-minute delay would have a negative impact on operations. Current wake turbulence standards are adequate. 1992CLOSED – Unacceptable Action
1990A-90–077 Alter AC 90-23D to advise small aircraft pilots taking off behind large aircraft to expect a 3-minute delay. A 3-minute delay is unnecessary based on studies conducted by the FAA and industry. 1992CLOSED – Unacceptable Action
1993A-93-017 Advise operators of the L-1011 airplane of the necessity of adjusting seat belts tightly on cockpit observer seats. FAA issued ACOB No. 8-94-3 to this effect. 1994CLOSED – Acceptable Action
1993A-93-137 Develop realistic gust loads for the design of future large transport planes. FAA published an increase design loads criterion for engine pylons but not for other components and multi-axis gusts. 1997CLOSED – Unacceptable Action
1993A-93-141 Modify departure routes at Anchorage during periods of severe mountain induced turbulence. Not possible to modify procedures due to limited amount of available airspace. 1994CLOSED – Acceptable Action
1993A-93-142 Use the WSR-88d Doppler weather radar at Anchorage for greater forecasting accuracy of mountain-generated turbulence forecasts. Done, as of January 1996. 1998CLOSED – Acceptable Action
1993A-93-171 Complete a design review of the Twin Commander Model 690A to assess aileron functioning in cold weather and turbulence. Review done; no problems found. Twin Commanders inspected to assure that ailerons were rigged properly. 1995CLOSED – Acceptable Action
1994A-94-042 Establish 4, 5 and 6 NM separation for large, medium and small airplanes taking off behind a B757. FAA considers 4-mile separation for all aircraft following a B757 adequate. 1995CLOSED – Unacceptable Action
1994A-94-043 Revise airplane weight classification scheme to feature separation standards for four weight categories instead of three. FAA: “Analysis and assumptions that led to … the safety and operational efficiency of the three-weight classification system” will be unchanged. Pilots and air traffic controllers to receive more training in wake turbulence avoidance. 1999CLOSED – Acceptable Alternate Action
1994A-94-044 Establish a 3-degree glide path for a landing B757 when other airplanes are in trail. Done in June 1996 by change to aeronautical information manual (AIM). 1999CLOSED – Acceptable Action
1994A-94-045 Instruct pilots of B757 aircraft of the importance of maintaining a 3-degree glide slope. FAA issued Flight Standards Handbook Bulletin (HBAT) 94-17 which addresses pilot training and awareness in issues raised by the Safety Board’s recommendation. 1995CLOSED – Acceptable Action
1994A-94-046 Prohibit a VFR clearance to an IFR airplane behind a heavy airplane until the pilot can maintain the minimum IFR separation. FAA issued change to Order 7110.65 requiring controllers to consider wake turbulence and closure rates when applying visual separation between aircraft. 1994CLOSED – Acceptable Alternate Action
1994A-94-047 Require controllers to advise a following airplane if a heavy airplane is ahead of them on descent to land in order to avoid wake turbulence. FAA published change that provides advisories when an aircraft is 5 NM or closer to a B757 or other heavy jet. 1999CLOSED – Acceptable Action
1994A-94-048 Require arriving VFR airplanes that have been sequenced behind a heavier jet to be advised in order to minimize wake turbulence. FAA published change that provides advisories when an aircraft is 5 NM or closer to a B757 or other heavy jet. 1999CLOSED – Acceptable Action
1994A-94-049 Require air traffic controllers to issue type of aircraft ahead in landing pattern to following aircraft as a means of increasing awareness of wake turbulence hazard. Done. 1995CLOSED – Acceptable Action
1994A-94-050 Implement annual refresher training for controllers on wake turbulence separation. FAA developed a training video. 1999CLOSED – Acceptable Action
1994A-94-051 Develop guidance in Airman’s Information Manual to ensure that following airplane remains above leading airplane in landing pattern. Done.AC 90-233, “Aircraft Wake Turbulence,” revised to include the information recommended. 2002CLOSED – Acceptable Action
1994A-94-052 Expand guidance in Airman’s Information Manual to define vertical movement of wake vortex flow field. In 2000, the FAA modified its Wake Vortex Training Aid. 2002CLOSED – Acceptable Action
1994A-94-053 Require airline (Part 121) and air taxi (Part 135) operators to provide training in wake vortex avoidance and separation distances. Distribution of Wake Vortex Training Aid and Flight Standards Information Bulletin (FSIB) meet the intent of the recommendation. 1996CLOSED – Acceptable Action
1994A-94-054 Revise pilot practical test standards to emphasize wake turbulence avoidance. Appropriate revisions published. 1995CLOSED – Acceptable Action
1994A-94-055 Conduct additional flight tests of B757 to determine the persistence and strength of wake vortices. Done at Memphis Airport. Not done at JFK because of funding limitations. 1999CLOSED – Acceptable Action
1994A-94-056 Require wake vortex measurement during new-design aircraft certification. 5 pages of letters back and forth between the NTSB and the FAA. NTSB declared it was “disappointed” at FAA response. FAA said “it is difficult to establish an airworthiness requirement for wake vortex characteristics.” 2005OPEN – Acceptable Response

(NTSB noted the recommendation “is over 10 years old”)

1994A-94-057 Require reporting of wake vortex encounters and capture on flight data recorders (FDRs) relevant information. FAA will collect ASRS [Aviation Safety Reporting System] data for 1 year in 1995 to assess if additional collection efforts are necessary. 1995CLOSED – Unacceptable Action
1994A-94-058 Continue to sponsor research to reduce the wake vortex hazard. Done. 1994CLOSED – Acceptable Action
1994A-94-059 Determine if the traffic collision and avoidance system (TCAS) is appropriate for providing pilots with separation distance to avoid wake turbulence. FAA working with RTCA [Radio Technical Commission for Aeronautics] to determine if “station keeping” is a possibility. 1996CLOSED – Acceptable Action
1994A-94-060 Encourage operators of smaller airplanes to use TCAS to confirm separation distance. RTCA to develop standards within next 3 years. 1996CLOSED – Acceptable Action
1994A-94-009 Issue an AD for B747s requiring inspection for wing spar fuse pins following an encounter with severe turbulence. FAA issued AD 92-24-51. 1996CLOSED – Acceptable Action
1994A-94-010 Review the service history of other airplane types to determine if similar inspections following severe turbulence should be conducted. FAA conducted such a review, and determined that inspection requirements in current maintenance procedures are sufficient. 1996CLOSED – Acceptable Action
1994A-94-037 Require MD-11 operators to be aware of potential damage to composite elevators following a severe turbulence encounter. McDonnell Douglas issued two All Operators Letters. FAA considers action complete. 1994CLOSED – Acceptable Action
1995A-95-005 Make design changes as necessary to Robinson R22 and R44 helicopters to prevent loss of control due to turbulence encounters. Controls deemed adequate. 1996CLOSED – Acceptable Action
1996A-96-084 Provide guidance on how children more than 24 months old are be to restrained during takeoffs, landings and during turbulence. FSIB issued to ask parents the age of their child (to ensure that children > 24 months are in a seat and not on their parent’s lap). 1996CLOSED – Acceptable Action

(Having all children/babies in their own seat with belts would be more appropriate; this recommendation perpetuates the insanity of “lap” children)

1998A-98-105 Re-emphasize to pilots the importance of reporting turbulence that may affect the safety of other flights. FAA agrees and published an AC 91-74, “Pilot Guide – Flight in Icing Conditions” in 2002.. 2003CLOSED – Acceptable Action
1999A-99-011 Re-examine design of seat belt buckles to ensure they remain latched during turbulence. FAA estimates rate of seat belt failures is 1.9 per billion seat-hours, “which does not support regulatory action to require … replacement.”SAIB issued on D-ring seat belt anchors. 2004CLOSED – Acceptable Alternate Action

(Classification is mystifying; use of automobile-style pushbutton latch would provide greater safety and uniformity among transportation modes.)

2003A-03-041 Review and revise maintenance inspection criteria following severe turbulence encounters. FAA forming an industry working group to develop “best practices” within a year. 2008OPEN – Acceptable Response

From the table above a number of inferences can be made:

— Deaths are a much greater stimulus for NTSB recommendations than injuries. The recommendations are the result predominantly of fatal crashes.

— Of the 46 turbulence-related recommendations issued, 19 (41%) deal with the cruise phase, where most injuries occur. If the number of deaths and injuries in cruise were considered, the order probably should be reversed, with 60% of the recommendations addressed to the cruise phase of flight.

— Of the two “OPEN” recommendations, none deal with passenger or crew safety during turbulence.

— Of the 18 “CLOSED” recommendations concerning turbulence in cruise, some have been overtaken by events, others are airplane specific and only one (A-73-002) deals with interior design to reduce injuries.

— No NTSB recommendations deal with flimsy overhead bin latches coming open during turbulence and spilling their contents onto passengers sitting below.

— None of the NTSB recommendations address the chronic problem of standing flight attendants being injured or killed during turbulence. From 1980 to 2008, more flight attendants than passengers were injured by turbulence, 184 to 114.

— None of the NTSB recommendations address the continued failure of all passengers to remain buckled up while seated.

— None of the recommendations address galley carts in the aisles. One can envision a means to secure them: a track in the floor, and a foot-pedal operated upside-down “T” fitting on the bottom of the cart to anchor it when stationary. Coffee pots could be secured by straps (coffee pots have been known to fly about during turbulence, scalding passengers).

— None of the NTSB recommendations address the dangerous practice of “lap children,” despite the history of such children being hurled to their injury or death during in-flight turbulence.

— None of the recommendations address cockpit-cabin crew coordination when turbulence is expected.

The NTSB claims it has a 90%-95% acceptance rate for its recommendations. In the area of turbulence, it has about an 80% acceptance rate, under the generous allowance that if the action was closed by the NTSB for even the flimsiest reasons advanced by the FAA, that recommendation counted towards the overall acceptance rate.

It is also evident, from the recent injuries on the United Airlines flight over Missouri that the successfully implemented NTSB recommendations have had, at most, about 10% effectiveness at reducing injuries during cruise overall and none during that particular flight. Indeed, one could argue that NTSB recommendations issued over the past 30 years have had nil effect on reducing injuries during in-flight cruise.

The FAA has done the easy things that cost little, thereby garnering a high acceptance rate to the NTSB recommendations. The difficult efforts that require money tend to generate a huge amount of delaying correspondence and result in either a slow death to the recommendation or it being held in an “OPEN” status by the NTSB in the slim hope of implementation.

The NTSB may wish to reconsider the process of generating recommendations. It seems that many are “down in the weeds,” offering much in the way of detailed, tactical advice. Meanwhile, the major issues – such as aircraft certification (see A-94-056) – which seem straightforward, languish in a miasma of “do nothingness.”

Average time for recommendation to be classified “CLOSED – Acceptable Action” is on the order of four years. The longest period to acceptance is 18 years. Given that most of the recommended actions in this category are simple, the time seems excessive and not behooving of a pro-active safety culture at the FAA. Then again, the sheer volume of NTSB recommendations has to be taken into account. Fewer, more strategic NTSB recommendations might reduce the workload at the FAA – at a “cost” to the NTSB of a lower percentage of “CLOSED – Acceptable Action” about which to crow.


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