{"id":28898554,"date":"2026-10-20T16:24:59","date_gmt":"2026-10-20T14:24:59","guid":{"rendered":"https:\/\/migflug.com\/afterburner\/faa-ad-boeing-737ng-horizontal-stabilizer-freeplay-flutter-2026\/"},"modified":"2026-10-20T16:25:47","modified_gmt":"2026-10-20T14:25:47","slug":"faa-ad-boeing-737ng-horizontal-stabilizer-freeplay-flutter-2026","status":"publish","type":"post","link":"https:\/\/migflug.com\/afterburner\/it\/faa-ad-boeing-737ng-horizontal-stabilizer-freeplay-flutter-2026\/","title":{"rendered":"Boeing 737NG Flutter Risk: FAA Orders Stabilizer Freeplay Checks"},"content":{"rendered":"<style>.et_pb_title_container h1.entry-title { padding-top: 40px !important; }<\/style>\r\n\r\n<!-- mfsh:top -->\r\n\r\n<style>\r\n.mfsh-trigger{display:inline-flex;align-items:center;gap:10px;height:44px;padding:0 18px;margin:0 0 26px;border:2px solid 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Not inspect it for cracks. Measure the play &mdash; the free movement in the pivot hinges that carry the horizontal stabilizer and in the jackscrew that drives it. Several airlines had reported their aircraft oscillating in pitch, and when the FAA traced the reports back, the answer was wear.<\/p>\r\n\r\n<p>Airworthiness directives are routine. Boeing airframes collect dozens a year, most of them dull. This one is worth reading because of the single sentence the FAA uses to justify it, and because of what the agency told four operators who asked for a little more time.<\/p>\r\n\r\n\r\n<div style=\"background:#f4f6f9;border-left:4px solid #5C91FF;padding:18px 22px;margin:28px 0\"><p style=\"margin:0 0 10px;font-weight:700;color:#0d1117;font-size:17px\">Quick Facts<\/p><p style=\"margin:4px 0\"><strong>Directive:<\/strong> FAA AD 2026-20-14 (Amendment 39-23487), Docket FAA-2025-5403, published 19 October 2026<\/p><p style=\"margin:4px 0\"><strong>Aircraft:<\/strong> Boeing 737-600, -700, -700C, -800, -900 and -900ER &mdash; 1,987 of US registry<\/p><p style=\"margin:4px 0\"><strong>Trigger:<\/strong> Reports from multiple operators of pitch oscillation events<\/p><p style=\"margin:4px 0\"><strong>Unsafe condition:<\/strong> Excessive horizontal stabilizer freeplay, which the FAA says could lead to a flutter event and loss of control<\/p><p style=\"margin:4px 0\"><strong>Required action:<\/strong> Measure freeplay at the stabilizer pivot hinges and the jackscrew, then repair or replace worn parts as the findings dictate<\/p><p style=\"margin:4px 0\"><strong>Effective date:<\/strong> 23 November 2026<\/p><p style=\"margin:4px 0\"><strong>Cost:<\/strong> 6 work-hours, about 510 dollars per aeroplane; roughly 1.01 million dollars across US operators<\/p><p style=\"margin:4px 0\"><strong>Service information:<\/strong> Boeing Alert Requirements Bulletin 737-55A1104 RB, 12 June 2025<\/p><\/div>\r\n\r\n\r\n<h2 style=\"padding-top:22px\">What the Directive Actually Requires<\/h2>\r\n\r\n<p>AD 2026-20-14, Amendment 39-23487, applies to Boeing 737-600, -700, -700C, -800, -900 and -900ER series airplanes &mdash; the Next Generation family, not the MAX. The FAA estimates it affects <strong>1,987 airplanes of United States registry<\/strong>. The worldwide figure is larger, because American ADs bind American operators and other regulators then decide whether to mirror them, which for a Boeing product they almost always do.<\/p>\r\n\r\n<p>The work itself is short. Operators must measure the freeplay of the left and right horizontal stabilizer pivot hinges and of the jackscrew, following Boeing Alert Requirements Bulletin 737-55A1104 RB of 12 June 2025, and then do whatever the measurement tells them to do: determine total stabilizer freeplay, repeat the measurement, or repair or replace worn parts. The bulletin sets the compliance times. The directive becomes effective on 23 November 2026.<\/p>\r\n\r\n<p>Under the Air Transport Association chapter system this is ATA 55, Stabilizers &mdash; which is to say, the structure that holds the aeroplane&rsquo;s nose where the crew put it. The FAA&rsquo;s statement of the unsafe condition is three lines long and does not hedge.<\/p>\r\n\r\n\r\n<div style=\"background:#f8f9fa;border-left:4px solid #d32f2f;padding:20px 22px;margin:18px 0 24px;font-size:16px;line-height:1.7\"><em>&ldquo;This AD was prompted by reports from multiple operators of pitch oscillation events due to excessive horizontal stabilizer freeplay. The FAA is issuing this AD to address excessive horizontal stabilizer freeplay. The unsafe condition, if not addressed, could lead to a flutter event, which can result in loss of control of the airplane.&rdquo;<\/em><div style=\"margin-top:10px;font-size:14px;color:#555\"><strong>Federal Aviation Administration<\/strong> &mdash; Airworthiness Directive 2026-20-14, paragraph (e), Federal Register, 19 October 2026<\/div><\/div>\r\n\r\n\r\n<h2 style=\"padding-top:22px\">Freeplay Is Not a Defect. Too Much of It Is.<\/h2>\r\n\r\n<p>Every mechanical joint has clearance. A hinge bearing that gripped its pin with zero play would seize; a ballscrew with no backlash would bind. The 737&rsquo;s entire horizontal stabilizer is a moving surface, pivoting on hinges at the rear and driven in pitch trim by a jackscrew at the front, and both of those interfaces are designed with tolerances. New, they are small. After twenty years and sixty thousand cycles of a surface that loads and unloads on every rotation, every flare and every trim input, they are larger.<\/p>\r\n\r\n<p>Boeing&rsquo;s procedure measures four values &mdash; the bulletin calls them D1, D2, D3 and H &mdash; and compares them against what the service information labels Level 1 limits. Inside the limits, the aeroplane goes back to work. Outside, the operator either replaces the worn part or accepts an interim check, which Alaska Airlines described in its comment as falling due within 3,100 flight hours or six months of the last measurement, whichever comes first.<\/p>\r\n\r\n<p>The crews who filed the original reports would not have seen any of this. They would have felt the aeroplane hunting slightly in pitch, in a way a 737 does not normally hunt.<\/p>\r\n\r\n\r\n<figure class=\"wp-block-image size-large\" style=\"margin:0 0 24px;width:100%\"><svg viewBox=\"0 0 900 360\" width=\"100%\" style=\"display:block;background:#ffffff;border:1px solid #e2e7ee;height:auto\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" role=\"img\" aria-label=\"Diagram of Boeing 737 horizontal stabilizer freeplay and the difference between a damped and a divergent oscillation\"><style>.t{font:13px Montserrat,Helvetica,Arial,sans-serif;fill:#454e5e}.h{font:700 15px Montserrat,Helvetica,Arial,sans-serif;fill:#0d1117}.s{font:11px Montserrat,Helvetica,Arial,sans-serif;fill:#8a93a2}<\/style><text x=\"28\" y=\"34\" class=\"h\">The joint the FAA wants measured<\/text><text x=\"500\" y=\"34\" class=\"h\">Below and above the flutter boundary<\/text><rect x=\"28\" y=\"196\" width=\"150\" height=\"54\" fill=\"#eef2f7\" stroke=\"#cdd6e2\"\/><text x=\"40\" y=\"228\" class=\"t\">fuselage<\/text><polygon points=\"178,150 420,132 420,160 178,178\" fill=\"#dce7fb\" stroke=\"#5C91FF\" stroke-width=\"2\"\/><text x=\"266\" y=\"122\" class=\"t\">horizontal stabilizer<\/text><line x1=\"196\" y1=\"176\" x2=\"196\" y2=\"214\" stroke=\"#0d1117\" stroke-width=\"3\"\/><circle cx=\"196\" cy=\"174\" r=\"6\" fill=\"#ffffff\" stroke=\"#0d1117\" stroke-width=\"2\"\/><text x=\"150\" y=\"286\" class=\"t\">jackscrew<\/text><line x1=\"196\" y1=\"216\" x2=\"196\" y2=\"272\" stroke=\"#cdd6e2\" stroke-width=\"1\" stroke-dasharray=\"3 3\"\/><circle cx=\"402\" cy=\"156\" r=\"9\" fill=\"#ffffff\" stroke=\"#0d1117\" stroke-width=\"2\"\/><circle cx=\"402\" cy=\"156\" r=\"3\" fill=\"#0d1117\"\/><text x=\"352\" y=\"312\" class=\"t\">pivot hinges<\/text><line x1=\"402\" y1=\"166\" x2=\"402\" y2=\"298\" stroke=\"#cdd6e2\" stroke-width=\"1\" stroke-dasharray=\"3 3\"\/><polygon points=\"178,146 420,128 420,134 178,152\" fill=\"none\" stroke=\"#d8534f\" stroke-width=\"1.5\" stroke-dasharray=\"5 4\"\/><text x=\"236\" y=\"98\" class=\"t\" fill=\"#d8534f\">free movement with no load on it<\/text><text x=\"28\" y=\"340\" class=\"s\">Boeing measures four values, D1, D2, D3 and H, against Level 1 limits.<\/text><line x1=\"500\" y1=\"118\" x2=\"860\" y2=\"118\" stroke=\"#e2e7ee\"\/><polyline points=\"500,118 501.5,115.3 503,112.7 504.5,110.2 506,107.8 507.5,105.5 509,103.4 510.5,101.5 512,99.9 513.5,98.4 515,97.2 516.5,96.2 518,95.5 519.5,95.1 521,94.9 522.5,94.9 524,95.2 525.5,95.8 527,96.6 528.5,97.6 530,98.8 531.5,100.2 533,101.8 534.5,103.5 536,105.4 537.5,107.3 539,109.4 540.5,111.5 542,113.7 543.5,115.8 545,118 546.5,120.1 548,122.2 549.5,124.2 551,126.1 552.5,127.8 554,129.5 555.5,131 557,132.3 558.5,133.4 560,134.4 561.5,135.1 563,135.7 564.5,136.1 566,136.2 567.5,136.2 569,135.9 570.5,135.5 572,134.9 573.5,134.1 575,133.1 576.5,132 578,130.8 579.5,129.4 581,127.9 582.5,126.4 584,124.8 585.5,123.1 587,121.4 588.5,119.7 590,118 591.5,116.3 593,114.7 594.5,113.1 596,111.6 597.5,110.3 599,109 600.5,107.8 602,106.8 603.5,105.9 605,105.1 606.5,104.5 608,104.1 609.5,103.8 611,103.7 612.5,103.7 614,103.9 615.5,104.2 617,104.7 618.5,105.3 620,106.1 621.5,107 623,107.9 624.5,109 626,110.2 627.5,111.4 629,112.7 630.5,114 632,115.3 633.5,116.7 635,118 636.5,119.3 638,120.6 639.5,121.8 641,123 642.5,124.1 644,125.1 645.5,126 647,126.9 648.5,127.6 650,128.2 651.5,128.6 653,129 654.5,129.2 656,129.3 657.5,129.3 659,129.1 660.5,128.8 662,128.5 663.5,128 665,127.4 666.5,126.7 668,125.9 669.5,125.1 671,124.2 672.5,123.2 674,122.2 675.5,121.2 677,120.1 678.5,119.1 680,118 681.5,117 683,116 684.5,115 686,114.1 687.5,113.2 689,112.4 690.5,111.7 692,111 693.5,110.5 695,110 696.5,109.6 698,109.4 699.5,109.2 701,109.1 702.5,109.1 704,109.2 705.5,109.5 707,109.8 708.5,110.2 710,110.6 711.5,111.2 713,111.8 714.5,112.4 716,113.1 717.5,113.9 719,114.7 720.5,115.5 722,116.3 723.5,117.2 725,118 726.5,118.8 728,119.6 729.5,120.4 731,121.1 732.5,121.8 734,122.4 735.5,123 737,123.5 738.5,123.9 740,124.3 741.5,124.6 743,124.8 744.5,124.9 746,125 747.5,125 749,124.9 750.5,124.7 752,124.5 753.5,124.2 755,123.8 756.5,123.4 758,122.9 759.5,122.4 761,121.8 762.5,121.2 764,120.6 765.5,120 767,119.3 768.5,118.7 770,118 771.5,117.4 773,116.7 774.5,116.1 776,115.6 777.5,115 779,114.5 780.5,114.1 782,113.7 783.5,113.3 785,113 786.5,112.8 788,112.6 789.5,112.5 791,112.5 792.5,112.5 794,112.6 795.5,112.7 797,112.9 798.5,113.1 800,113.4 801.5,113.8 803,114.1 804.5,114.5 806,115 807.5,115.5 809,116 810.5,116.5 812,117 813.5,117.5 815,118 816.5,118.5 818,119 819.5,119.5 821,119.9 822.5,120.3 824,120.7 825.5,121.1 827,121.4 828.5,121.7 830,121.9 831.5,122.1 833,122.2 834.5,122.3 836,122.3 837.5,122.3 839,122.3 840.5,122.2 842,122 843.5,121.8 845,121.6 846.5,121.3 848,121 849.5,120.7 851,120.4 852.5,120 854,119.6 855.5,119.2 857,118.8 858.5,118.4 860,118\" fill=\"none\" stroke=\"#2e7d4f\" stroke-width=\"2\"\/><text x=\"500\" y=\"64\" class=\"t\">Tight joint: a disturbance dies away.<\/text><line x1=\"500\" y1=\"256\" x2=\"860\" y2=\"256\" stroke=\"#e2e7ee\"\/><polyline points=\"500,256 501.5,255.6 503,255.2 504.5,254.7 506,254.3 507.5,253.9 509,253.5 510.5,253.1 512,252.8 513.5,252.4 515,252.1 516.5,251.9 518,251.7 519.5,251.5 521,251.4 522.5,251.3 524,251.3 525.5,251.3 527,251.4 528.5,251.5 530,251.7 531.5,251.9 533,252.2 534.5,252.6 536,252.9 537.5,253.4 539,253.8 540.5,254.3 542,254.9 543.5,255.4 545,256 546.5,256.6 548,257.2 549.5,257.8 551,258.4 552.5,258.9 554,259.5 555.5,260 557,260.5 558.5,260.9 560,261.4 561.5,261.7 563,262 564.5,262.2 566,262.4 567.5,262.5 569,262.6 570.5,262.5 572,262.4 573.5,262.2 575,262 576.5,261.6 578,261.2 579.5,260.8 581,260.2 582.5,259.6 584,259 585.5,258.3 587,257.6 588.5,256.8 590,256 591.5,255.2 593,254.4 594.5,253.5 596,252.7 597.5,251.9 599,251.2 600.5,250.5 602,249.8 603.5,249.1 605,248.6 606.5,248.1 608,247.7 609.5,247.3 611,247.1 612.5,247 614,246.9 615.5,247 617,247.1 618.5,247.4 620,247.7 621.5,248.2 623,248.8 624.5,249.4 626,250.1 627.5,251 629,251.9 630.5,252.8 632,253.8 633.5,254.9 635,256 636.5,257.1 638,258.3 639.5,259.4 641,260.5 642.5,261.6 644,262.7 645.5,263.7 647,264.6 648.5,265.5 650,266.3 651.5,267 653,267.5 654.5,268 656,268.3 657.5,268.5 659,268.6 660.5,268.5 662,268.3 663.5,268 665,267.5 666.5,266.8 668,266 669.5,265.1 671,264.1 672.5,263 674,261.7 675.5,260.4 677,259 678.5,257.5 680,256 681.5,254.4 683,252.9 684.5,251.3 686,249.7 687.5,248.2 689,246.7 690.5,245.4 692,244 693.5,242.8 695,241.8 696.5,240.8 698,240 699.5,239.4 701,238.9 702.5,238.6 704,238.5 705.5,238.6 707,238.9 708.5,239.4 710,240.1 711.5,241 713,242.1 714.5,243.3 716,244.7 717.5,246.3 719,248 720.5,249.9 722,251.8 723.5,253.9 725,256 726.5,258.2 728,260.3 729.5,262.5 731,264.7 732.5,266.8 734,268.8 735.5,270.8 737,272.6 738.5,274.2 740,275.7 741.5,277 743,278.1 744.5,279 746,279.7 747.5,280.1 749,280.2 750.5,280 752,279.6 753.5,278.9 755,278 756.5,276.8 758,275.3 759.5,273.6 761,271.6 762.5,269.4 764,267 765.5,264.5 767,261.8 768.5,258.9 770,256 771.5,253 773,250 774.5,247 776,244 777.5,241.1 779,238.2 780.5,235.6 782,233 783.5,230.7 785,228.7 786.5,226.9 788,225.3 789.5,224.1 791,223.2 792.5,222.7 794,222.5 795.5,222.7 797,223.3 798.5,224.2 800,225.5 801.5,227.2 803,229.3 804.5,231.7 806,234.4 807.5,237.4 809,240.7 810.5,244.3 812,248 813.5,251.9 815,256 816.5,260.1 818,264.3 819.5,268.5 821,272.7 822.5,276.7 824,280.6 825.5,284.3 827,287.8 828.5,291 830,293.9 831.5,296.4 833,298.5 834.5,300.2 836,301.4 837.5,302.2 839,302.4 840.5,302.2 842,301.4 843.5,300.1 845,298.2 846.5,295.9 848,293 849.5,289.7 851,285.9 852.5,281.7 854,277.2 855.5,272.3 857,267.1 858.5,261.6 860,256\" fill=\"none\" stroke=\"#d8534f\" stroke-width=\"2\"\/><text x=\"500\" y=\"166\" class=\"t\">Slack joint at the same speed: the air<\/text><text x=\"500\" y=\"184\" class=\"t\">feeds the motion faster than the<\/text><text x=\"500\" y=\"202\" class=\"t\">structure can damp it. That is flutter.<\/text><text x=\"500\" y=\"340\" class=\"s\">Schematic. Not to scale.<\/text><\/svg><figcaption style=\"font-size:13px;color:#777;text-align:center;margin-top:6px;font-style:italic\">How wear at the stabilizer hinges and jackscrew turns into the condition the FAA is worried about. Original diagram, Afterburner.<\/figcaption><\/figure>\r\n\r\n\r\n<h2 style=\"padding-top:22px\">Flutter Is the Word That Matters<\/h2>\r\n\r\n<p>Flutter is the reason this directive exists, and it is the most unforgiving failure mode in structural aeronautics. It is not vibration in the ordinary sense. It is a self-feeding oscillation in which the airflow couples two of a structure&rsquo;s natural modes &mdash; classically bending and twisting &mdash; so that each cycle extracts more energy from the air than the structure&rsquo;s own damping can absorb. Below the flutter speed, a disturbance dies away. Above it, the same disturbance doubles, and doubles again, and the component departs the aeroplane. The whole sequence can run its course in seconds.<\/p>\r\n\r\n<p>Certification is supposed to put a wide margin between the fastest the aeroplane will ever go and the speed at which any of this can start. Freeplay eats into that margin, because a joint that can move without resistance behaves as a nonlinearity: the surface is free to begin oscillating on its own before the aerodynamic stiffness of the system has anything to push against. A structure with slack in it can enter a limit-cycle oscillation at speeds where the same structure, tight, is perfectly stable.<\/p>\r\n\r\n<p>That is why the FAA is not asking anyone to look for cracks. There is nothing broken to find. It is asking operators to measure how loose the joint has become, because looseness is the thing that moves the boundary.<\/p>\r\n\r\n\r\n<div style=\"position:relative;padding-bottom:56.25%;height:0;overflow:hidden;margin:24px 0\"><iframe class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" src=\"https:\/\/www.youtube.com\/embed\/qpJBvQXQC2M\" style=\"position:absolute;top:0;left:0;width:100%;height:100%;border:0\" allowfullscreen><\/iframe><\/div>\r\n\r\n\r\n<h2 style=\"padding-top:22px\">Four Operators Asked for Relief. The FAA Said No Four Times.<\/h2>\r\n\r\n<p>The proposal went out for comment in January and drew responses from nine parties. The Air Line Pilots Association, Boeing and two individuals supported it without change. Aviation Partners Boeing wrote in to confirm that its blended and split scimitar winglets, fitted under supplemental type certificate ST00830SE, do not get in the way of the inspection; the FAA agreed, and that was the only comment it accepted.<\/p>\r\n\r\n<p>The other four went nowhere. Canadian North asked for the first inspection to fall due at 36 months rather than 12, so it would land on a heavy maintenance visit instead of pulling aircraft out of service unscheduled. United Airlines argued that an aeroplane with brand-new hinge bearings should not be on the same repeat interval as one still flying original production parts. Alaska Airlines asked to be allowed to repair straight to the Level 1 limits instead of running interim checks. United also asked for credit for freeplay inspections it had already done under a 2022 Boeing multi-operator message with, by its own account, identical work instructions.<\/p>\r\n\r\n<p>The FAA disagreed with all four. On the intervals it was blunt: the repetitive checks &ldquo;were chosen to ensure that excessive freeplay does not exist for either original or new or replaced parts.&rdquo; Operators can still apply individually for an alternative method of compliance, which is the normal pressure valve. But as a fleet-wide matter, nobody got longer.<\/p>\r\n\r\n<h2 style=\"padding-top:22px\">What It Costs, and What It Says<\/h2>\r\n\r\n<p>Almost nothing, by the standards of airline maintenance. The FAA prices the freeplay measurement at six work-hours at 85 dollars an hour &mdash; 510 dollars an aeroplane, 1,013,370 dollars across the US fleet. A repeat measurement costs the same again. Replacing or repairing a worn part is costed at one work-hour, 85 dollars, plus parts the agency admits it cannot price: it has received, in its own words, no definitive data on which to base the estimate.<\/p>\r\n\r\n<p>A million dollars spread across every American 737NG operator is a rounding error. That is the point. The directive is cheap because measuring is cheap, and the FAA has decided that measuring 1,987 aeroplanes is a better trade than waiting to find out which one had the most wear. The agency closed the rule by noting that apart from minor editorial changes it was adopting the proposal exactly as written, and that none of the changes increase the economic burden on any operator.<\/p>\r\n\r\n<p>Operators have until 23 November to start, and Boeing&rsquo;s bulletin to tell them how soon after that each individual airframe is due. Most will fold it into work already scheduled. That is usually how the most serious-sounding directives end: not with aeroplanes grounded, but with a technician on a stand with a dial gauge, measuring a number that should be small.<\/p>\r\n\r\n<p><em>Sources: Federal Register Vol. 91 No. 200, 19 October 2026, pages 65959 to 65961 (FAA Airworthiness Directive 2026-20-14, FR Doc 2026-21333); aeroTELEGRAPH.<\/em><\/p>\r\n\r\n<!-- mfsh:bottom -->\r\n\r\n<button type=\"button\" class=\"mfsh-trigger mfsh-bottom\" data-mfsh-placement=\"bottom\" aria-haspopup=\"dialog\"><svg><use href=\"#mfsh-i-share\"\/><\/svg>Share this story<\/button>\r\n\r\n<!-- \/mfsh:bottom -->\r\n\r\n\r\n<style>.mfq{margin:34px 0 8px}.mfq h2{font:26px\/1.3 \"Gilroy semiBold\",Helvetica,Arial,sans-serif;color:#0d1117;padding-top:22px;margin:0 0 6px}.mfq .qa details{border-top:1px solid #5C91FF;margin:0;padding:0}.mfq .qa details:last-of-type{border-bottom:1px solid #e2e7ee}.mfq .qa summary{cursor:pointer;list-style:none;display:flex;justify-content:space-between;align-items:center;gap:16px;padding:22px 26px;font:18px\/1.7 \"Gilroy semiBold\",Helvetica,Arial,sans-serif;color:#0d1117}.mfq .qa summary::-webkit-details-marker{display:none}.mfq .qa summary::after{content:\"+\";font:24px Helvetica,sans-serif;color:#3568e0;flex:0 0 auto}.mfq .qa details[open] summary::after{content:\"\\2013\"}.mfq .qa details:hover summary{color:#3568e0}.mfq .qa .a{font:16px\/1.7 \"Gilroy regular\",Helvetica,Arial,sans-serif;color:#454e5e;padding:0 26px 24px}.mfq .qa .a a{color:#3568e0}@media(max-width:680px){.mfq .qa summary{padding:18px 14px;font-size:17px}.mfq .qa .a{padding:0 14px 20px}}<\/style>\r\n\r\n\r\n<section class=\"mfq\"><h2>Frequently Asked Questions<\/h2><div class=\"qa\"><details open><summary>What does FAA airworthiness directive 2026-20-14 require on the Boeing 737?<\/summary><div class=\"a\">AD 2026-20-14 requires operators to measure the freeplay of the left and right horizontal stabilizer pivot hinges and of the jackscrew on certain Boeing 737 Next Generation aircraft, following Boeing Alert Requirements Bulletin 737-55A1104 RB of 12 June 2025, and then to carry out whatever on-condition work the measurement calls for, including repairing or replacing worn parts.<\/div><\/details><details><summary>Which Boeing 737 models are affected by the horizontal stabilizer freeplay directive?<\/summary><div class=\"a\">The directive applies to Boeing 737-600, -700, -700C, -800, -900 and -900ER series airplanes. These are the Next Generation models. The 737 MAX family is not listed in the applicability paragraph, and neither are the earlier 737 Classic models.<\/div><\/details><details><summary>What is horizontal stabilizer freeplay?<\/summary><div class=\"a\">Freeplay is the amount a joint can move before it starts carrying load. On the 737 the whole horizontal stabilizer pivots on hinges and is driven in pitch trim by a jackscrew, and both interfaces are built with small clearances. Wear enlarges them. Boeing measures four values, called D1, D2, D3 and H, against published Level 1 limits.<\/div><\/details><details><summary>Why is flutter dangerous?<\/summary><div class=\"a\">Flutter is a self-feeding oscillation in which airflow couples two of a structure\u2019s natural modes, usually bending and twisting, and feeds in more energy each cycle than the structure can damp out. Below the flutter speed a disturbance dies away; above it, the motion grows until the component fails. The sequence can run its course in seconds, which is why certification keeps a wide margin from it.<\/div><\/details><details><summary>How many Boeing 737s does the directive affect, and what does it cost?<\/summary><div class=\"a\">The FAA estimates 1,987 airplanes of United States registry. It prices the freeplay measurement at six work-hours, about 510 dollars per aircraft, or 1,013,370 dollars across US operators. Replacing or repairing a worn part is costed at one work-hour plus parts, which the agency says it has no definitive data to estimate.<\/div><\/details><details><summary>Did airlines object to the Boeing 737 stabilizer inspection directive?<\/summary><div class=\"a\">Four operators asked for relief and all four were refused. Canadian North wanted the first inspection deferred from 12 to 36 months, United Airlines wanted longer repeat intervals for newly replaced hinge bearings and credit for earlier inspections, and Alaska Airlines wanted an alternative repair path. The Air Line Pilots Association and Boeing supported the proposal without change.<\/div><\/details><details><summary>When does the Boeing 737 stabilizer freeplay directive take effect?<\/summary><div class=\"a\">The directive is effective on 23 November 2026. From that date the compliance times in Boeing Alert Requirements Bulletin 737-55A1104 RB run against the effective date of the AD rather than against the original issue date of the bulletin, and individual aircraft become due according to that schedule.<\/div><\/details><\/div><\/section>\r\n\r\n\r\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"What does FAA airworthiness directive 2026-20-14 require on the Boeing 737?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"AD 2026-20-14 requires operators to measure the freeplay of the left and right horizontal stabilizer pivot hinges and of the jackscrew on certain Boeing 737 Next Generation aircraft, following Boeing Alert Requirements Bulletin 737-55A1104 RB of 12 June 2025, and then to carry out whatever on-condition work the measurement calls for, including repairing or replacing worn parts.\"}},{\"@type\":\"Question\",\"name\":\"Which Boeing 737 models are affected by the horizontal stabilizer freeplay directive?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The directive applies to Boeing 737-600, -700, -700C, -800, -900 and -900ER series airplanes. These are the Next Generation models. The 737 MAX family is not listed in the applicability paragraph, and neither are the earlier 737 Classic models.\"}},{\"@type\":\"Question\",\"name\":\"What is horizontal stabilizer freeplay?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Freeplay is the amount a joint can move before it starts carrying load. On the 737 the whole horizontal stabilizer pivots on hinges and is driven in pitch trim by a jackscrew, and both interfaces are built with small clearances. Wear enlarges them. Boeing measures four values, called D1, D2, D3 and H, against published Level 1 limits.\"}},{\"@type\":\"Question\",\"name\":\"Why is flutter dangerous?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Flutter is a self-feeding oscillation in which airflow couples two of a structure\u2019s natural modes, usually bending and twisting, and feeds in more energy each cycle than the structure can damp out. Below the flutter speed a disturbance dies away; above it, the motion grows until the component fails. The sequence can run its course in seconds, which is why certification keeps a wide margin from it.\"}},{\"@type\":\"Question\",\"name\":\"How many Boeing 737s does the directive affect, and what does it cost?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The FAA estimates 1,987 airplanes of United States registry. It prices the freeplay measurement at six work-hours, about 510 dollars per aircraft, or 1,013,370 dollars across US operators. Replacing or repairing a worn part is costed at one work-hour plus parts, which the agency says it has no definitive data to estimate.\"}},{\"@type\":\"Question\",\"name\":\"Did airlines object to the Boeing 737 stabilizer inspection directive?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Four operators asked for relief and all four were refused. 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From that date the compliance times in Boeing Alert Requirements Bulletin 737-55A1104 RB run against the effective date of the AD rather than against the original issue date of the bulletin, and individual aircraft become due according to that schedule.\"}}]}<\/script><div style=\"background:#f0f4ff;border-left:4px solid #5C91FF;padding:16px 20px;margin:32px 0 8px\"><p style=\"margin:0 0 8px;font-weight:600;color:#333\">Related Posts<\/p><p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/boeing-737-max-10-faa-certification-imminent-type-certification-board-2026\/\">Boeing 737 MAX 10 certification moves to the final board<\/a><\/p><p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/faa-737-max-vnav-software-glitch-not-safety-concern-max-10-2026\/\">The FAA and the 737 MAX VNAV software glitch<\/a><\/p><p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/why-airlines-cannot-stop-ordering-the-boeing-737-even-after-everything\/\">Why airlines cannot stop ordering the Boeing 737<\/a><\/p><\/div>\r\n","protected":false},"excerpt":{"rendered":"<p>Share this story &ldquo;Pitch oscillation&rdquo; is one of those phrases that sounds mild right up until you read what the Federal Aviation Administration thinks it can turn into. On Monday the agency published a final rule ordering operators of almost two thousand American-registered Boeing 737s to go and measure the slop in the aeroplane&rsquo;s tailplane. [&hellip;]<\/p>\n","protected":false},"author":26,"featured_media":28898534,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"editor_notices":[],"footnotes":""},"categories":[665,670],"tags":[],"class_list":["post-28898554","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-aviation-world","category-news"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Boeing 737NG Horizontal Stabilizer Freeplay AD | MiGFlug<\/title>\n<meta name=\"description\" content=\"Excessive horizontal stabilizer freeplay has the FAA ordering checks on 1,987 US-registered Boeing 737NGs, with flutter and loss of control the stated risk.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" 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